Contrary to popular belief, Arnold does not wear a kilt, but instead dons a plaid shirt that hangs out of his blue sweater and a hat that only covers a small part of his football-shaped head.
Arnold (voiced by Toran Caudell in season 1 and six episodes in season 2, Phillip Van Dyke in seasons 2 and 3, Spencer Klein in seasons 4 and 5, and Alex D. Linz in April Fool's Day and The Journal) – The nine-year-old protagonist and title character of the series. Arnold tends to daydream from time to time. He lives in a boarding house with his grandparents. The fate of his parents is unknown. Arnold has had two major crushes in the series: one with sixth-grader Ruth McDougal (through most of season 1), and one with a classmate named Lila Sawyer (introduced in season 2). Arnold's most catalytic relationship is with his classmate Helga Pataki. Helga is secretly in love with him, though to keep these feelings secret she bullies Arnold. Arnold seems unaware of this fact for most of the series, other than the occasional hint from Helga and other classmates. Helga's secret was revealed to Arnold during the Hey Arnold! movie, but Arnold gave Helga the opportunity to refute her confession, attributing it to "the heat of the moment". According to series creator Craig Bartlett, had the canceled "Jungle Movie" sequel been animated, Arnold would have returned Helga's feelings with a kiss of his own, with his best friend interrupting the moment. Arnold is friends with most of his fellow fourth-graders, with the best of which being Gerald Johanssen, whose relationship dates as far back as preschool. Arnold's surname is never revealed on the show and the mystery surrounding his full name became a running gag on the show, by the last name almost being revealed, then someone or something interrupting or otherwise preventing it from being heard.
Grandpa Phillip (Phil/Steely Phil) (voiced by Dan Castellaneta) – Arnold's cheery, fun-loving grandfather. He is 81 years old, as of the episode "Grandpa's Birthday". Arnold often comes to him for advice. He often tells Arnold stories about his past experiences, although he has a tendency to stretch the truth. Despite responding frivolously to Arnold's problems, he will often provide good wisdom. He is a World War II veteran and claims to have single-handedly won the Battle of the Bulge by tricking a large troupe of Nazi soldiers into eating numerous cans of spoiled CHAM, thereby poisoning them and creating a hole in the enemy line for the American troops to break through. Arnold does not believe his story at first, but it is later proven when Phil shows him a small monument of him hidden in some bushes in a park in Washington D.C. Phil was also a master at Chinese checkers in his youth, which earned him the nickname "Steely Phil". He is very healthy for his age, as well as athletic.
Grandma Gertrude (Gertie/Pookie) (voiced by Tress MacNeille) – Arnold's wacky but wise grandma who is often seen doing outlandish things, including dressing up and acting like fictional and historic figures, such as Calamity Jane. She is called "Pookie" by Grandpa Phil. She has a black belt. She and Phil had a similar relationship that Helga and Arnold have when they were kids (though her antics were a bit more vicious and extreme).
Arnie (voiced by Grant Hoover) – Arnold's cousin, who lives in the countryside and strongly resembles Arnold. He likes to collect lint and gum, count things, read the ingredients on the back of food containers, and makes a peculiar snorting sound on occasion. When he visits PS. 118, Lila develops a crush on him and attempts to attract his attention, but he develops an unrequited crush on Helga. He is often seen as strange, gross, dull or stupid by those around him.
Miles and Stella (voiced by Craig Bartlett and Antoinette Stella) – Arnold's parents. They are adventurous and brave, though Miles appears to be clumsy and tends to end up hurt. They met while exploring in San Lorenzo, where they occasionally crossed paths with the Green-Eyed people, a mysterious indigenous tribe. They returned to the city after Arnold's birth, but were called back for 'a final mission' when a friend informed them that the Green Eyes were in trouble: they failed to return, leaving their son presumably orphaned. Arnold comes across a journal detailing some of their adventures years afterwards. His pet pig, Abner, was a wedding gift to his parents from the Green Eyes.
Aunt Mitzi (voiced by Phyllis Diller) – Arnold's great aunt, Phil's twin sister and childhood rival. She is 81 years old.
Grandpa Phil's father (voiced by Dan Castellaneta) – He is often seen in Grandpa's flashbacks to the 1920s.
Grandpa Phil's grandfather (voiced by Dan Castellaneta) – He is seen in one of Grandpa's flashbacks. Grandpa remembers doing chores one winter while his friends were ice skating, only to be hit with a snowball by his grandfather who gave him permission to stop his chores and play.
Oskar Kokoshka (voiced by Steve Viksten) – A lazy, self-centered con artist, presumably an immigrant from an Eastern European country (in one episode he is referred to as being Czechoslovakian), that remains unemployed through most of the series until becoming a paperboy. He is disliked by pretty much everybody in the boarding house, especially Ernie Potts. His voice resembles that of comedian Yakov Smirnoff and he occasionally utters Smirnoff's catchphrases. He shares his name with an Austrian artist.
Suzie Kokoshka (voiced by Mary Scheer) – Oskar's loving and caring wife, who puts up with all of her husband's antics and laziness, though the two occasionally fight.
Mai Hyunh – Mr. Hyunh's long lost daughter (who never lived with her father in Sunset Arms). She only appears in the Christmas episode. It is revealed in the episode that she had been given to American troops during the Fall of Saigon.
Mr. Smith – A mysterious character who lived in the boarding house. Very secretive. His face is never seen, nor his voice has ever been heard. Only in the first season he is seen.
Lana Vail (voiced by Christine Ebersole) – A lawyer who resides in the boarding house. She wears a purple suit and has brown hair. She was a minor character to begin with, and has brief appearances throughout the series.
Mr. Purdy – he is only mentioned once in the episode "Gerald Comes Over" when Arnold collects the rent money.
Gerald Martin Johanssen (voiced by Jamil Walker Smith) – An African-American nine-year-old boy and Arnold's best friend. A fairly athletic boy who is portrayed as loyal, though much less responsible than Arnold.
Martin Johanssen (voiced by Rick Fitts) – Gerald's sometimes strict father, complains about wasting electricity. He is a Vietnam War veteran.
Mrs. Johanssen (voiced by Shari Belafonte) – Gerald's very kind mother, keeps family together. She is a cashier at the neighbourhood market.
Timberly Johanssen (voiced by Avriel Epps and Francesca Smith) – Gerald's little sister. She usually causes trouble due to her desire for attention or naturally childish behaviour. Unlike all the other children on the show, Timberly seems to age throughout the series. In her first appearance, she is four years old, but she already attends the first grade in "Timberly Loves Arnold", although this may be a continuity error, rather than intentional.
Helga Pataki, in her signature pink and red dress and pink bow
Helga G. Pataki (voiced by Francesca Smith) – Helga is nine years old and in the fourth grade. She constantly bullies her classmate Arnold to hide her true feelings of love for him. She is a talented writer and occasionally expresses interest in pursuing it as a career. She is neglected by her parents and often calls them by their first names because she does not think they are worthy of being called "Mom" and "Dad". She resents her overachieving, perfectionist older sister, Olga. Once in a while Helga will show a very small amount of love for her sister, as in the episode "Olga Gets Engaged", when she intervenes on Olga's behalf, saving her from what would have been a bad marriage, and "Big Sis" when she reveals her jealousy of Olga's relationship with Lila. Helga is an insecure person and puts on a mean, tomboyish front, making her the school bully.
Robert "Big Bob" Pataki (voiced by Maurice LaMarche) – Olga and Helga's oafish, ambitious entrepreneur father, a successful beeper salesman who owns a beeper store. He has extremely high expectations for Helga and frequently compares her to her older sister Olga. Bob also frequently calls Helga by Olga's name by mistake. However, Bob does care for Helga as is evidenced in subtle ways. Bob has difficulty showing his emotions for Helga since she and he always come into conflict with each other. He often mistakenly calls Arnold "Alfred".
Miriam Pataki (voiced by Kath Soucie) – Olga and Helga's inattentive mother. There are implications that Miriam suffers from alcoholism, as she often drinks "smoothies", forgets things, speaks in a slow, tired voice, has had her driver's license revoked, has to do community service and sleeps a lot (often in inappropriate places). The unaired Hey Arnold! spin-off, The Patakis, would have included her struggle with alcoholism and joining of Alcoholics Anonymous as a plot point. However, in one episode when Bob injures his back and can't work, Miriam fills in for him. During the episode Miriam sobers up and holds the fort. Miriam also becomes more attentive towards Helga until she becomes a workaholic and realizes that she is ignoring Helga. Then, she quits and makes Bob return to work. However, her sobriety doesn't last long because in episodes following this one, she is back to drinking smoothies. Miriam was a champion bull rider before marrying Bob, and she used to be an Olympic class swimmer. She reveals in the episode "Olga Gets Engaged" that she regrets marrying Bob.
Olga Pataki (voiced by Nika Futterman) – Helga's intelligent, outgoing, beautiful older sister, who attends Wellington College (fictional, as Wellington College, UK, is actually a secondary school). But in one of the episodes, Helga says that Olga attends Bennington College, which is an existing college located in the U.S. state of Vermont. Olga clearly suffers from perfectionism. She attended P.S. 118 as a child, and is praised by Helga's current teachers for her achievement. Bob and Miriam consider Olga to be perfect, which bothers Helga. There are times where her parents will confuse Helga for Olga. Fortunately, Olga does give Helga more attention than their parents much of the time and has good intentions. However, Helga does not receive Olga's attention or intentions very well and often tries to push Olga away and keep her distance. Olga has a tendency to view life through rose colored glasses and appears not to notice Helga's avoidance tactics. Therefore, either Olga likes to avoid conflict since she rarely acknowledges her family's problems, is oblivious, or in denial. It is revealed in the episode "Helga on the Couch" that Olga through the years has reacted to her family's problems by being a perfectionist and keeping quiet about the situations at hand.
Phoebe Heyerdahl (voiced by Anndi McAfee) – The smartest girl in the class. She is Helga's confidant. Her ethnicity is half-Japanese, but she is from Kentucky. Throughout the series, both she and Gerald have a love interest in one another.
Harold Berman (voiced by Justin Shenkarow) – A Jewish American school bully and friend of Arnold. He is 13 years old and overweight and in later episodes it is revealed that Harold has a soft spot. Despite his teasing and bullying tendencies, Harold is often revealed to be rather cowardly and usually cries for his mother whenever he gets scared or upset. He is sometimes referred to by the derisive nickname "fat boy." His best friends are Sid and Stinky.
Jerry Berman (voiced by David Wohl) – Harold's father. He has a tendency of talking in a very low pitch.
Marilyn Berman (voiced by Kath Soucie) – Harold's mother. She is more vocal with her scolding of Harold than her husband.
Eugene Horowitz (voiced by Christopher Castile for eight episodes, then Jarrett Lennon, then Benjamin Diskin in 1997–2000) – A somewhat socially inept but optimistic friend of Arnold, the class jinx. Eugene is prone to several forms of misfortune and is often bullied. He believes Arnold is a jinx due to several of his past tragedies having occurred in Arnold's presence.
Nate Horowitz (voiced by Michael Jeter) – Eugene's father. He is equally unlucky as his son as seen in the episode "Fishing Trip", in which he appears.
Rhonda Wellington Lloyd (voiced by Olivia Hack) – A rich yuppie girl, pompous, self-proclaimed fashion queen and friend of Arnold. She is one of the wealthiest children at P.S. 118. Both of her parents are stereotypically preppy.
Brooke Lloyd (voiced by Lori Alan) – Rhonda's mother who believes her daughter is a perfect angel who can do no wrong.
Lila Sawyer (voiced by Ashley Buccille) – A nice girl who came from a fictional farming community she calls "Pleasantville" and who lives with her father. Her mother is never seen or mentioned. She is Arnold's crush. However, she only prefers Arnold as a friend. She had a crush on Arnold's cousin Arnie. She knows that Helga loves Arnold and offered to help Helga become more like her in one episode.
Lila's Father (voiced by Dan Butler) – Lila's father is seen in the episode "Ms. Perfect". He appears to be a kind and caring father. When Lila is new to P.S. 118 and being bullied by some of her classmates, her father tries to be there for her. In the episode it is revealed that he had been unemployed and it ends happily with him getting a job.
Sidney "Sid" (voiced by Sam Gifaldi) – A friend of Arnold and one of Harold's best friends with paranoid tendencies. He is always shown wearing a green baseball cap backwards, a black leather jacket, and white Beatle boots. He often tells urban legends, with or without the assistance of Gerald. Perhaps his most well-known characteristic is that he typically ends up in ridiculous situations, such as becoming severely mysophobic; deciding to devote his life to Arnold after Arnold saves his life,among other things.
Stinky Peterson (voiced by Christopher Walberg) – Stinky is a tall and lanky friend of Arnold's from Arkansas, and he is also one of Harold's best friends. Stinky has a southern accent and a love for lemon pudding. His friendship with Harold had him originally portrayed in the first season as a bully and sidekick of Harold's who wore spiked wristbands, though the former was later de-emphasized and he was reinvented as a more affectionate, mild mannered and romantic character viewed as the class "ladies man", as he is romantically attracted to several female characters. He is shown to make up excellent poems while Phoebe is feeling depressed.
Thaddeus "Curly" Gammelthorpe (voiced by Adam Wylie) – The class psychopath. He has had meltdowns and outbursts throughout the show such as in the episodes "False Alarm" and "Curly Snaps". He also appears to have a major crush on Rhonda. In the episode "Curly's Girl", Rhonda pretends to be Curly's girlfriend for a week, but she is disgusted by his appeal.
Torvald (voiced by Michael Bacall) – A fourth grader who was held back for several years and is considerably older than the rest of the students. He is tutored by Arnold in one episode. In the episode "Tutoring Torvald", he is revealed to be 13 years old.
Sheena (voiced by Francesca Smith) – A geeky girl who does not like violence. Her aunt Shelly is the school nurse, her uncle Earl rows a boat.
Iggy (voiced by Joseph Ashton) – A friend of Arnold's who was popular until his classmates found out he wears bunny pajamas in "Arnold Betrays Iggy". His shirt tails stick out like Arnold's, creating illusion of a kilt. He almost always wears dark sunglasses that he rarely takes off.
Brainy (voiced by Craig Bartlett) – A geek and Helga's stalker who is usually knocked unconscious by Helga without Helga looking at him. He seems to be romantically attracted to her. He has a very deep voice, wheezes noisily, and never talks in a completed sentence. He rarely appears except when Helga looks at her locket containing a picture of Arnold. Apparently Brainy has not told anybody else about Helga's crush on Arnold.
Nadine Lowenthal (voiced by Lauren Robinson) – A young entomologist and Rhonda's best friend. She tends to find a lot of Rhonda's more stuck up opinions ridiculous. In the episode "Dinner for Four" she sets cockroaches free in a restaurant as a favour for Helga. This is the only episode where she has a bigger role than Rhonda, for her usual role is Rhonda's satellite character. In "Parents Day", Nadine is shown to be half black and half white.
Park (voiced by Marcus Toji) – A close friend of Arnold and others. In the episode "Longest Monday", it is revealed he has a secret hideout. He only speaks in seasons 1–3.
Joey Stevenson (voiced by Justin Shenkarow in earlier appearances, Michael Fishman in later appearances) – An African American boy who is easy to remember by knowing he is missing a tooth. He appears with Arnold's group of friends from time to time, though his most prominent roles are in the first season, when he was part of Harold's circle of friends, along with Iggy, Stinky, and Sid.
"Chocolate Boy" (voiced by Jordan Warkol) – A boy obsessed with chocolate. In "Chocolate Boy", it is revealed he eats chocolate because his nanny fed him large amounts of chocolate before she left to a "far away land called Delaware." Arnold helps break Chocolate Boy of his obsession, but he only becomes as equally over-excessive eating radishes as a replacement.
Wolfgang (voiced by Toran Caudell) – The main bully of the block who is a fifth grader and Arnold's nemesis. He also runs the fifth grade and leads the other fifth grade bullies in their troublemaking against younger students.
Edmund (voiced by Tim Wiley) – Wolfgang's best friend and sidekick. He often asks stupid questions, causing Wolfgang to remark "Shut up, Ed."
Mickey (voiced by Marty York) – A fifth grader who is nicknamed "The Weasel" as seen in "Longest Monday."
Gloria (voiced by Francesca Smith) – A girl who looks like Helga, but is more girly and has a nicer personality. Her first appearance is in "Magic Show" as a dream vision, but she is revealed to be a reality in "Helga's Boyfriend" when Stinky begins dating her, and appears as an extra in "Cool Party".
Ruth P. McDougal (voiced by Lacey Chabert) – A sixth grade girl who is Arnold's first crush.
Patricia "Big Patty" Smith (voiced by Danielle Judovits) – An ill-tempered sixth grade girl who becomes Harold's friend (it is implied that the two may have romantic feelings for each other as well). She beats up Helga when she falls victim to her pranks (intended for Lila). In a later episode she plans to fight Helga but stages it instead. She even asks Helga if she and Arnold had feelings for each other, which Helga denies. In season 4, she becomes friends with Rhonda after they both attend the same finishing school together. She was also held back a couple of years and is 14 years old.
Dr. Bliss (voiced by Kathy Baker) – A child psychologist who evaluates the students of P.S. 118 for a day and later becomes Helga's psychoanalyst. Also the second known character that is told by Helga that she loves Arnold. This character only appeared in one episode titled "Helga on the Couch."
Mr. Frank – A sixth-grade teacher, who is quite bored with his job.
Lieutenant Major Goose (voiced by John Garry) – Arnold's teacher for short time (after Miss Slovak and before Mr. Simmons), a martinet. He also was Martin Johanssen's drill sergeant during Vietnam War in "Veterans Day" episode.
Lunch lady (voiced by Kath E. Soucie and Danica Ivancevic) – A woman in charge of the school cafeteria. She is stereotypically brash in appearance, but sensitive to criticism of the cafeteria food.
Mr. Packenham (voiced by Daniel Stern) – A fifth grade teacher. He appears in "What's Opera, Arnold?" when he chaperons Arnold's class trip to the Opera and in "Phoebe Skips" when Phoebe is promoted to his class.
Rex Smythe-Higgins – Wealthy British child of an esteemed family, rival to Arnold.
Mr. Bailey (voiced by Vincent Schiavelli) – A worker of the Hall of Records. His first appearance is in the Christmas Special, where Arnold comes to him to help find Mr. Hyunh's daughter, Mai. His second appearance is in the series' feature film, where he helps in trying to find the document of the "Tomato Incident". When he can't find it, he tells Arnold about a man who keeps all kinds of historic records.
Mayor Dixie (voiced by Tress MacNeille) – The female mayor of Hillwood. In Hey Arnold!: The Movie, she allows Scheck to redevelop Arnold's neighborhood, even though the city council rejected the idea. When she is shown Scheck destroying the document of the "Tomato Incident", she decides to make it a historic landmark once again.
Mrs. Vitello (voiced by Elizabeth Ashley and Kath E. Soucie) – The owner of the neighborhood flower shop.
Councilman Marty Green (voiced by James Keane) a dedicated butcher and a politician. He has two brothers, Dave and Benji, and a son who is a vegetarian.
Mickey Kaline (voiced by Ron Perlman) – A retired baseball star and Arnold's favorite player. Arnold caught his final home run ball. After retirement he ran his own baseball-themed restaurant, Mickey's Dog Pound. He is based on two famous baseball players, Mickey Mantle and Al Kaline.
Dino Spumoni (voiced by Dean Corso, singing voice provided by Michael Levin) – A Dean Martin and Frank Sinatra-type singer, who faked his own death to increase his fame, which backfired because of Dino-Mania, an impersonator, who went so far as to ask to be called Dino, and started to date his ex-wife Candy Maldonado.
Don Reynolds (voiced by Harvey Korman) – A man who is former Dino Spumoni's partner who wrote lyrics for him.
Alphonse Perrier du von Scheck (voiced by Paul Sorvino) – A greedy developer who tries to tear down the neighborhood so he can build a mall, but is thwarted by Arnold, Helga, and Gerald. He serves as the main antagonist of Hey Arnold!: The Movie.
Stoop Kid (voiced by Danny Cooksey) – A kid who lives on a stoop and never leaves it until episode "Stoop Kid", when Arnold coaxes Stoop Kid to finally have the courage to leave his stoop. The only other times Stoop Kid is seen off of his stoop are in the episodes "Arnold Betrays Iggy", where Stoop Kid is seen in the crowd of people near the end of the episode, "Eugene, Eugene!", when he is seen in the audience during the school's musical, and "Cool Party" when he is a guest at Arnold's 'geek' party.
Willie, the Jolly Olly Man (voiced by Dan Castellaneta) – An ice cream man who is most often referred to as the "Jolly Olly Man," Willie is the driver of an ice cream truck that is frequently seen driving around Arnold's town. Throughout the series, he has been depicted as unfriendly, deranged, depressed, and hated by his father (who happens to be his employer). In one episode, he was the umpire at a baseball game Arnold and his friends played against the fifth graders.
Eduardo (voiced by Carlos Alazraqui) – Eduardo is an anthropologist from a fictional Central American Republic of San Lorenzo. He was friends with Arnold's parents, Miles and Stella, and helped them during their expeditions in San Lorenzo. He is the last person to ever talk to Arnold's parents before they disappeared into the dense jungles.
Harvey (voiced by Lou Rawls) – Mailman who delivers mail and seems to occasionally give advice. He dislikes snow.
Abner (vocal effects provided by Craig Bartlett) – Arnold's pet pig. He a gift from the Green-eyed People at Miles and Stella's wedding from a water basket. Phil first thought to cook Abner but Stella decided to keep the pig. Abner was mistaken for a girl by Stella, who wanted to name "her" Abigail.
Parrot was purchased by Bob Pataki so that he could train it to repeat quotes for his beeper commercials. However, he soon becomes frustrated when the parrot won't remain quiet when he watches a game show in his bedroom. Instead of bringing the parrot downstairs, he inconsiderately places it in Helga's bedroom. When Helga recites a love poem pertaining to Arnold in her sleep, the parrot instantly absorbs it and begins to repeat it. Helga became upset the next morning when she heard the parrot repeat the poem as well as her name at the end. When Helga tried to grab the parrot from its enclosure, it managed to fly out of her bedroom window and soon falls into Arnold's care.
Monitor Lizard was purchased by Helga who had followed Arnold and his grandfather into a pet store. Earlier in the episode, Arnold had found a parrot and decided to take care of it until he could find its owner. However, he was unaware that the parrot had belonged to Bob Pataki. Once Helga learned that Arnold had her father's parrot she made several attempts to snatch the bird before it would reveal her name after reciting her poem. The only reason that Helga purchased the monitor lizard was so that Arnold wouldn't know that she was following him and trying to snatch the parrot from him. After she purchased the lizard, she left it in Phoebe's care. But during show and tell the following day at school, Phoebe brought in the monitor lizard in the hopes that Helga would take it back. However, the monitor lizard ate the parrot that Arnold brought to class before it could reveal her name. After the monitor lizard ate the parrot, Helga replied "We're going to be good friends." The monitor lizard never appears in any other episodes.
Cupcake, also known as Thurston, is a kitten that was discovered by Arnold and Harold in the episode titled "Harold's Kitty". After the kitten's discovery, Harold decides to keep the kitten but Arnold disagrees. Arnold decides to make flyers in case the kitten has an owner who is looking for it. Meanwhile, Harold becomes increasingly attached to the kitten that he named Cupcake and becomes upset when he discovers that Arnold made missing flyers of the kitten. Eventually an elderly woman by the name of Mrs. Ryle contacts Arnold to let him know that she is the rightful owner of Cupcake whom she had named "Thurston". When Arnold and Mrs. Ryle arrive at Harold's parents' house, he refuses to give up the kitten and the police are called for intervention. Harold's parents eventually arrive home after they were out and fail to convince him to return the kitten to its rightful owner. After Arnold has a heart to heart discussion with Harold, he finally agrees to return the kitten to Mrs. Ryle. After Mrs. Ryle receives the kitten, she agrees to let Harold come to her house and play with the kitten from time to time. This makes Harold very happy and the episode ends with him playing with the kitten at Mrs. Ryle's house. Cupcake did not appear in any other episodes.
Chester was Arnold's Carrier Pigeon that appeared in the episode titled "Pigeon Man". Chester appeared at the beginning of the episode returning a note to Arnold. However, Chester appeared to be lethargic and not acting quite right. Arnold's friends began talking about the pigeon man which prompted Gerald to share some information he had received through the grape vine about pigeon man. After Gerald finished talking, Arnold decided to bring Chester to the pigeon man in the hopes that he could help Chester feel better. After meeting the pigeon man who looked at Chester, it was decided that he should spend some time with the pigeon man. Arnold stopped by to visit the pigeon man and check up on Chester's progress. Arnold also spent some time with the lonely pigeon man. Eventually Chester recovered and was able to return home with Arnold. Chester never appeared in any other episodes.
Henry was Eugene's pet Goldfish and appeared in the episode titled "Eugene's Pet". Eugene brought Henry to school with him for show and tell but when it was Arnold's turn, he began performing tricks with his yo yo which detached from its string and accidentally struck Henry who died instantly. Throughout the episode, a guilt ridden Arnold tries to make things up to Eugene and goes so far as to adopt an Angel Fish at the local aquarium in Eugene's name. But when Eugene briefly looked away, Arnold saw a shark eat his newly adopted fish and decides not to tell him. When Eugene looked back at the tank and saw another Angel Fish, he thought it was his and knew none the wiser.
Pooter was a Scottish Terrier that appeared in the episode titled "Grandpa's Sister". Pooter was a family pet that belonged to Arnold's grandfather and great aunt Mitzi when they were children. Phil and Mitzi loved their dog very much and would spend time with him. While Phil and Mitzi were playing in the backyard, Pooter dug a large hole and got out. Phil and Mitzi looked everywhere for Pooter and called his name. By the time they found him, he'd been hit by a Milk Truck. The twins took Pooter to the Vet, but it was too late and there was nothing he could do. Pooter was put to sleep on November 13, 1927. Phil and Mitzi buried Pooter in the back yard. Phil and Mitzi blamed each other for Pooter's death and stopped talking to each other for 71 years.
Lurkey was a turkey that appeared in a picture at Stinky Peterson's house in the episode titled "Stinky's Pumpkin". Lurkey was a turkey that belonged to Stinky's father as a child and was ultimately served for Thanksgiving dinner.
Pinky was a worm that belonged to one of Arnold's classmates named Billy in the episode titled "Eugene's Bike". Later on in the episode Pinky got loose from its enclosure and was unintentionally squashed by Helga as she walked towards her desk.
^ abcdefghi"Helga on the Couch". Hey Arnold!. Season 4. Episode 16. December 4, 1999. Nickelodeon.
^ ab"Crush on Teacher". Hey Arnold!. Season 2. Episode 14. December 14, 1997. Nickelodeon. "Oh, how I long to match Arnold's stride, run with him as one, break the tape at the finish line of life as Mrs. Arnold... Wait, what is his last name?"
^ ab"The Journal". Hey Arnold!. Season 5. Episode 19–20. November 11, 2002. Nickelodeon.
^ ab"Eugene, Eugene!". Hey Arnold!. Season 4. Episode 21. January 28, 2003. Nickelodeon.
^ abcd"Grandpa's Birthday". Hey Arnold!. Season 3. Episode 7. September 30, 1998. Nickelodeon.
^"24 Hours to Live". Hey Arnold!. Season 1. Episode 19. February 3, 1997. Nickelodeon. "Hey grandpa, I've got a problem. [...] What should I do?"
^ abc"Veterans Day". Hey Arnold!. Season 4. Episode 15. November 6, 1999. Nickelodeon.
^"Steely Phil". Hey Arnold!. Season 2. Episode 12. November 30, 1997. Nickelodeon.
^"Mugged". Hey Arnold!. Season 1. Episode 9. December 2, 1996. Nickelodeon.
^"Girl Trouble". Hey Arnold!. Season 3. Episode 19. January 4, 1999. Nickelodeon.
^ ab"Grandpa's Sister". Hey Arnold!. Season 4. Episode 12. October 16, 1999. Nickelodeon.
^"Sally's Comet". Hey Arnold!. Season 1. Episode 16. January 13, 1997. Nickelodeon.
^ ab"Snow". Hey Arnold!. Season 1. Episode 6. November 11, 1996. Nickelodeon.
^"Oskar Gets a Job". Hey Arnold!. Season 3. Episode 9. October 14, 1998. Nickelodeon.
^"Arnold as Cupid". Hey Arnold!. Season 1. Episode 10. December 9, 1996. Nickelodeon.
^ ab"Heat". Hey Arnold!. Season 1. Episode 6. November 11, 1996. Nickelodeon. "Nobody's knocking down any walls, you hot-headed loony."
^"Mr. Hyunh Goes Country". Hey Arnold!. Season 3. Episode 2. September 2, 1998. Nickelodeon.
^ ab"Arnold's Christmas". Hey Arnold!. Season 1. Episode 11. December 11, 1996. Nickelodeon.
^"Door #16". Hey Arnold!. Season 1. Episode 10. December 9, 1996. Nickelodeon.
^"Helga's Makeover". Hey Arnold!. Season 1. Episode 4. October 16, 1996. Nickelodeon.
^"The Little Pink Book". Hey Arnold!. Season 1. Episode 2. October 9, 1996. Nickelodeon.
^ abc"Olga Comes Home". Hey Arnold!. Season 1. Episode 16. January 13, 1997. Nickelodeon.
^ abc"Olga Gets Engaged". Hey Arnold!. Season 3. Episode 5. September 16, 1998. Nickelodeon.
^"Big Sis". Hey Arnold!. Season 5. Episode 3. March 18, 2000. Nickelodeon.
^"Spelling Bee". Hey Arnold!. Season 1. Episode 15. January 6, 1997. Nickelodeon.
^ abc"Quantity Time". Hey Arnold!. Season 2. Episode 12. November 30, 1997. Nickelodeon.
^"Girl Trouble". Hey Arnold!. Season 3. Episode 19. January 4, 1999. Nickelodeon. "Hey, Helga, you in there? It's your little friend Alfred on the phone!"
^ ab"The Beeper Queen". Hey Arnold!. Season 4. Episode 4. March 29, 1999. Nickelodeon.
^"Helga and the Nanny". Hey Arnold!. Season 3. Episode 10. October 19, 1998. Nickelodeon.
^ ab"Road Trip". Hey Arnold!. Season 3. Episode 7. September 30, 1998. Nickelodeon. "In case you haven't noticed, Phoebe, Miriam isn't exactly World's Greatest Mom material. [...] What kind of a mother packs your lunch with plastic silverware, moist towelettes, and no sandwich, or takes impromptu naps behind the sofa while I'm starving to death, or constantly forgets to pick me up from soccer practice?"
^ ab"Magic Show". Hey Arnold!. Season 1. Episode 19. February 3, 1997. Nickelodeon.
^"Harold's Bar Mitzvah". Hey Arnold!. Season 2. Episode 15. December 21, 1997. Nickelodeon.
^ ab"Harold's Kitty". Hey Arnold!. Season 2. Episode 3. October 5, 1997. Nickelodeon.
^ ab"Harold the Butcher". Hey Arnold!. Season 3. Episode 1. August 31, 1998. Nickelodeon.
^ ab"Phoebe's Little Problem". Hey Arnold!. Season 5. Episode 24. June 8, 2004. Nickelodeon.
^"Arnold's Hat". Hey Arnold!. Season 1. Episode 3. October 14, 1996. Nickelodeon. "Out of my way, fat boy!"
^"Eugene's Birthday". Hey Arnold!. Season 4. Episode 3. March 17, 1999. Nickelodeon.
^ ab"Fishing Trip". Hey Arnold!. Season 5. Episode 15. April 27, 2002. Nickelodeon.
^"Rhonda Goes Broke". Hey Arnold!. Season 5. Episode 10. January 5, 2001. Nickelodeon.
^ abcd"Ms. Perfect". Hey Arnold!. Season 2. Episode 6. October 26, 1997. Nickelodeon.
^ ab"School Play". Hey Arnold!. Season 3. Episode 20. March 8, 1999. Nickelodeon.
^"Sid and Germs". Hey Arnold!. Season 5. Episode 6. April 19, 2000. Nickelodeon.
^"Arnold Saves Sid". Hey Arnold!. Season 2. Episode 8. November 2, 1997. Nickelodeon.
^"False Alarm". Hey Arnold!. Season 1. Episode 18. January 27, 1997. Nickelodeon.
^"Curly Snaps". Hey Arnold!. Season 3. Episode 6. September 23, 1998. Nickelodeon.
^"Curly's Girl". Hey Arnold!. Season 5. Episode 18. October 14, 2002. Nickelodeon.
^"Tutoring Torvald". Hey Arnold!. Season 1. Episode 14. December 30, 1996. Nickelodeon.
^ ab"Eugene's Bike". Hey Arnold!. Season 1. Episode 1. October 7, 1996. Nickelodeon.
^"Rhonda's Glasses". Hey Arnold!. Season 2. Episode 13. December 7, 1997. Nickelodeon.
^ ab"Wheezin' Ed". Hey Arnold!. Season 1. Episode 13. December 23, 1996. Nickelodeon.
^"Rich Kid". Hey Arnold!. Season 3. Episode 18. December 28, 1998. Nickelodeon.
^ ab"Arnold Betrays Iggy". Hey Arnold!. Season 3. Episode 10. October 19, 1998. Nickelodeon.
^"Helga's Love Potion". Hey Arnold!. Season 2. Episode 2. September 28, 1997. Nickelodeon.
^"Best Friends". Hey Arnold!. Season 2. Episode 11. November 23, 1997. Nickelodeon.
^"Dinner for Four". Hey Arnold!. Season 4. Episode 5. March 31, 1999. Nickelodeon.
^"Parents Day". Hey Arnold!. Season 5. Episode 8. April 12, 2000. Nickelodeon.
^ ab"Longest Monday". Hey Arnold!. Season 2. Episode 4. October 12, 1997. Nickelodeon.
^"Chocolate Boy". Hey Arnold!. Season 5. Episode 12. January 26, 2001. Nickelodeon.
^"New Bully on the Block". Hey Arnold!. Season 5. Episode 5. April 12, 2000. Nickelodeon.
^"Operation Ruthless". Hey Arnold!. Season 1. Episode 7. November 18, 1996. Nickelodeon.
^"Hey Harold!". Hey Arnold!. Season 3. Episode 11. October 21, 1998. Nickelodeon.
^ ab"Helga vs. Big Patty". Hey Arnold!. Season 3. Episode 4. September 9, 1998. Nickelodeon.
^"Polishing Rhonda". Hey Arnold!. Season 4. Episode 10. September 25, 1999. Nickelodeon.
^"Principal Simmons". Hey Arnold!. Season 5. Episode 4. April 5, 2000. Nickelodeon.
^ ab"Phoebe Skips". Hey Arnold!. Season 5. Episode 5. March 31, 1999. Nickelodeon.
^ abc"New Teacher". Hey Arnold!. Season 2. Episode 1. September 21, 1997. Nickelodeon.
^"What's Opera, Arnold?". Hey Arnold!. Season 2. Episode 17. January 4, 1998. Nickelodeon.
^ ab"Coach Wittenberg". Hey Arnold!. Season 2. Episode 16. December 28, 1997. Nickelodeon.
^"Benchwarmer". Hey Arnold!. Season 1. Episode 12. December 16, 1996. Nickelodeon.
^"Part-Time Friends". Hey Arnold!. Season 3. Episode 17. December 7, 1998. Nickelodeon.
^"Mr. Green Runs". Hey Arnold!. Season 5. Episode 2. March 11, 2000. Nickelodeon.
^ ab"Dangerous Lumber". Hey Arnold!. Season 3. Episode 2. September 2, 1998. Nickelodeon.
^"Preteen Scream". Hey Arnold!. Season 3. Episode 6. September 23, 1998. Nickelodeon.
^"Monkeyman!". Hey Arnold!. Season 5. Episode 1. March 4, 2000. Nickelodeon.
^ ab"Pigeon Man". Hey Arnold!. Season 1. Episode 15. January 6, 1997. Nickelodeon.
^"School Dance". Hey Arnold!. Season 3. Episode 19. January 4, 1999. Nickelodeon.
^"Stoop Kid". Hey Arnold!. Season 1. Episode 3. October 14, 1996. Nickelodeon.
^"Cool Party". Hey Arnold!. Season 3. Episode 21. November 2, 1998. Nickelodeon.
^"Abner Come Home". Hey Arnold!. Season 1. Episode 17. January 20, 1997. Nickelodeon.
^"Eugene's Pet". Hey Arnold!. Season 2. Episode 4. October 12, 1997. Nickelodeon.
^"Stinky's Pumpkin". Hey Arnold!. Season 4. Episode 3. March 17, 1999. Nickelodeon.