The Watterson family, depicted outside their home; from left to right, clockwise: Gumball, Nicole, Richard, Anais and Darwin.
Gumball Watterson (voiced by Logan Grove, seasons 1–2; Jacob Hopkins, season 3 onward) – Gumball is a blue 12-year-old cat who lives with his family in the fictional American city of Elmore. He attends Elmore Junior High in the seventh grade along with his adoptive brother and best friend Darwin. Gumball's antics often end up getting him into trouble. Despite his rambunctious behavior, however, he is depicted as loyal, serious and kindhearted. A recurring theme throughout the series is his crush on his schoolmate Penny Fitzgerald, who in turn shares the same feelings for him – however, they both struggle to properly express their feelings for each other.
Darwin Watterson (voiced by Kwesi Boakye, seasons 1-2; Terrell Ransom, Jr., season 3 onward) – Darwin, a goldfish, is Gumball's best friend and adoptive brother. Initially given to Gumball as a pet, Darwin later sprouted legs and subsequently became a full member of the Watterson family. Due to his sudden introduction into the world, he tends to be more naïve and gullible than other characters. He is easily fascinated and scared by simple things. Although Gumball can sometimes be a negative influence on him, Darwin is extremely loyal to Gumball and often helps him out of sticky situations.
Anais Watterson (voiced by Kyla Rae Kowalewski) – A pink rabbit, Anais is Gumball and Darwin's 4-year-old sister. She is incredibly smart for her age, to the point that she attends Elmore Junior High with her brothers. Gumball resents the fact that she is always telling him what to do, but nonetheless loves her and acknowledges her good intentions. Although impatient with her brother, she often tags along with him on his misadventures as a voice of reason, usually having to help Gumball out of situations caused by these misadventures. She has, however, been shown to not be above manipulating her family to get what she wants. Despite her intellectuality, she still shows typical childlike behavior and has tried to fit in with Gumball and Darwin on numerous occasions.
Nicole Watterson (voiced by Teresa Gallagher) – Nicole is a blue cat who is responsible for the upkeep of her family, performing house chores and working long hours at The Rainbow Factory. A workaholic, she is often over-stressed and possesses a short temper. She acts as a guide to her children Gumball and Darwin when they get in a tough spot with their misadventures. Competitive by nature, Nicole is a master martial artist, and is very agile and flexible.
Richard Watterson (voiced by Dan Russell) – A pink rabbit and stay-at-home dad, Richard spends most of his time sleeping, eating, and watching television. Named "the laziest person in Elmore" since 1983, he has a large appetite and is a voracious eater. Richard often serves as a third-wheel to his sons' misadventures and cares deeply for his family despite his lethargic nature. He does not appear to have much sense of responsibility or intelligence; nonetheless, he usually has meaningful and constructive intentions.
Several Elmore Junior High students gathered in the school cafeteria. The series features a variety of different animals and objects for characters such as Gumball and his classmates.
Penny Fitzgerald (voiced by Teresa Gallagher) – Penny is a living peanut with antlers growing out of her head who is Gumball's primary love interest in the series. She returns Gumball's affections, but both are incapable of expressing their feelings for one another. Their attempts to kiss each other have twice been hampered by last-minute events, such as Richard honking his car in "The Date" and Banana Joe chopping down a tree house in "The Pressure". Penny's father is extremely overprotective of his daughter, and does not trust Gumball until he saves her from getting run over by his own car in the episode "The Knights". She is member of the Elmore Junior High cheerleading and synchronized swimming teams.
Tobias Wilson (voiced by Rupert Degas, season 1; Hugo Harrison, season 2 onward) – Tobias is a multicolored humanoid who is heavily interested in sports and possesses an overbearing self-confidence. He thinks of himself as a heavily built jock, despite actually being rather weak, and appears to be quite wealthy. He makes his debut appearance in "The Third", where Gumball and Darwin pay him ten dollars to become their friend. In "The Knights", Tobias holds a mock medieval battle with Gumball for the affection of Penny. Despite this, he has been seen hanging out with Gumball and Darwin on several occasions, including having a starring role in one of the duo's home movies. He has an older sister, Rachel (voiced by Jessica McDonald), who considers herself of higher status than Tobias and his "dweeb loser baby friends".
Banana Joe (voiced by Rupert Degas, season 1; Hugo Harrison, season 2 onward) – A hyperactive banana, Banana Joe is the class clown of Elmore Junior High and has the tendency to crack a joke whenever possible. His jokes often serve as a source of irritation to others, with Gumball describing him as a "one-trick pony" in his debut appearance.
Carrie Krueger (voiced by Jessica McDonald) – Carrie is an emo ghost and self-described "punk rock chick" who lives in a malevolent mansion and "enjoys being depressed." She has the abilities to teleport and possess living bodies, and in "The Ghost" she uses the latter ability on Gumball in order to feel the satisfaction of being able to eat again. In "Halloween", she turns the Watterson siblings into ghosts so they can attend a ghost-exclusive Halloween party at her mansion, and in the process almost gets them trapped in the Underworld.
Tina Rex (voiced by Dan Russell) – A Tyrannosaurus who lives in the Elmore city junkyard, Tina is the Elmore Junior High school bully. She often picks on her fellow schoolmates, especially Gumball, and has her own gang of bullies which includes Jamie and, to his reluctance, Anton. As a dinosaur, she is the strongest person in school, contributing to her fearsome and aggressive reputation. Despite this, she also has a softer side not only in general, but also for Gumball; in the episode "The Fight" she reveals that she considers him to be a friend. Her official Cartoon Network biography suggests that "perhaps she's just angry at the world for not noticing her femininity."
Bobert (voiced by Kerry Shale) – One of the smartest students at Elmore Junior High, Bobert is a robot who constantly struggles to understand emotion and develop a social life. He is the primary focus of the episode "The Robot", where Darwin and Gumball's efforts to help him fit in ultimately end with him stealing the latter's identity. Multiple times in the series, he has showcased his ability to transform into a much larger form by triggering his "defense mode". In the episode "The Bet", he is forced to become Gumball's personal slave for a day after losing a bet.
Carmen (voiced by Alix Wilton Regan) – Carmen is a cactus who is considered to be a leader among her female classmates. She is in a relationship with her balloon classmate Alan, though the danger of her spikes bursting him is a constant hindrance. Their relationship annoys their classmates, who are frequently annoyed by their romantic gestures and deem them "too perfect". They briefly break up in "The Storm" after Gumball accidentally kisses Carmen, but he succeeds in getting them back together by the end of the episode.
Alan (voiced by Rupert Degas, season 1; Hugo Harrison, season 2 onward) – Alan is a teal colored balloon who, despite their physical incompatibility, deeply loves Carmen. He is overly nice and even-tempered, never showing anger or raising his voice even when the subject of insults or physical attacks, much to the annoyance of his classmates. Being filled with helium, Alan regularly speaks in a high-pitched voice.
Masami (voiced by Jessica McDonald) – A living cloud, Masami is the wealthy daughter of the Rainbow Factory's owner. Spoiled by her parents, she is prone to tantrums and has threatened to have her classmates' parents fired should she not have her way. When angry, she has the ability to develop into a full storm cloud capable of causing mass amounts of damage. The episode "The Storm" reveals her unrequited crush on Alan, and she manipulates Gumball into getting the two together, albeit temporarily.
Leslie (voiced by Kerry Shale) – Leslie is an effeminate, friendly daisy who plays flute in the school band and can often be found hanging around the girls. He is Penny's cousin, and Gumball's mistaken assumption that he is her boyfriend is his major source of jealousy in the episode "The Flower".
Teri (voiced by Teresa Gallagher) – Teri is a hypochondriac paper bear, and as a result of her condition is usually be found in the nurse's office. Although somewhat self-absorbed and paranoid, she is very nice and is one of the school's cheerleaders. Her mother works as a doctor and maintains a website discussing the dangers of germs.
Hector Jotunheim (voiced by Kerry Shale) – Hector is a massive but gentle giant who is the largest student in Elmore Junior High, to the point that only his legs and feet are seen. Hector is the subject of the episode "The Colossus", where his mother – a witch who works as a cleaning lady – reveals that he can be dangerous if he expresses too much emotion, such as anger, sadness or excitement. In the same episode, he goes on a rampage around Elmore after Gumball and Darwin, unaware of Hector's need to control his emotions, describe him as being too boring. His surname is a reference to Jötunheimr, the homeland of giants in Norse mythology.
Juke (voiced by Beatbox Hobbit) – A native of the continent of Boomboxemburg who moved to Elmore, Juke is, as described by Gumball, a "boombox head" who speaks entirely in beatboxing. As a result, nobody in Elmore Junior High can understand him. He is able to speak comprehensible English if he is switched from "Music Mode" to "Voice Mode" through a button on the back of head, but his arms are too short to reach the button and his attempts to communicate this fact to others end in failure.
Anton (voiced by Lewis MacLeod) – Anton is a simple-minded piece of toast who was forcibly drafted into Tina's gang despite his unwillingness to do so, and only appeases them to avoid their anger.
Idaho (voiced by Rupert Degas, season 1; Hugo Harrison, season 2 onward) – A free-spirited potato from the rural countryside with old-fashioned beliefs, Idaho is one of the less popular students of Elmore Junior High. In "The Bumpkin", Gumball, disillusioned with his suburban lifestyle, seeks Idaho's help in teaching his family how to live a simple lifestyle. However, Gumball eventually finds himself unable to resist his modern lifestyle, and one night Idaho walks in on him indulging in video games and junk food. Gumball talks him into trying out his modern lifestyle and eventually sends him into severe culture shock, which his rural family cure by digging him in soil.
Sussie (voiced by Aurelie Charbonnier) – Sussie is an upside-down chin with googly eyes and puppet-like characteristics. She is talkative, odd, and obnoxious, and as a result is generally avoided by the rest of her classmates.
Clayton (voiced by Rupert Degas, season 1; Max Cazier, season 2 onward) – Clayton is a red ball of clay who is a compulsive liar, with a tendency of making up absurd stories about himself. In the episode "The Skull", Clayton begins an on-and-off friendship with Gumball and Darwin, and displays his ability to transform into different people and objects. At the end of the episode, he tells Principal Brown the truth for the first time.
Ocho (voiced by Max Cazier) – Ocho is an 8-bit spider and a generally friendly person, but often overreacts to what people say about him in a negative manner, such as to Darwin and Gumball after the latter accidentally sends him an insulting text message. In the show's first season, he spoke solely in video game blips; since the second season, however, he has started speaking in comprehensible, albeit distorted, English.
The Eggheads (voiced by Rupert Degas and Lewis MacLeod, season 1; Hugo Harrison and Lewis MacLeod, season 2 onward) – Two of the most intelligent students at Elmore Junior High, the Eggheads are a duo of nerdy eggs who are brothers who speak in prominent English accents and consider themselves to be much smarter than their classmates. They are not very popular, and as such are members of the "Reject Club" with Bobert and Ocho.
Jamie (voiced by Jessica McDonald) – Jamie is a "half-cow, half-troglodyte" creature who is a member of Tina's bullying gang. As a result of Miss Simian holding her back a year, she has grown resentful of her new classmates and of authority in general.
William (internal monologue narrated by Mic Graves) – William is a flying eyeball who is Miss Simian's personal spy and only talks when reporting information to her. The episode "The Voice" reveals that he has psychic abilities, which he uses to wreak havoc on Gumball and Darwin after they accidentally block him on the social networking site Elmore Plus. The same episode shows that he actually expresses a desire to interact with his classmates, which is hindered by his lack of a mouth; his inner thoughts are narrated to the viewers.
Sarah (voiced by Jessica McDonald) – A transferee to Elmore Junior High, Sarah is a yellow ice cream cone who debuted in the show's second season and makes her most prominent appearance in "The Sweaters", where she attempts to defend Gumball and Darwin from two uptight human students.
Rob (voiced by Hugo Harrison) – One of the less prominent Elmore Junior High students, Rob is a tall blue cyclops. He tries to have some friendly conversation with Gumball and Darwin in "The Pony", only to discover – much to his annoyance – that the two do not even know his name.
Molly Collins (voiced by Jessica McDonald) – A shy sauropod, Molly appeared most prominently in the show's first season. As shown in "The Pressure", she is the owner of a treehouse where she and the other girls hang out in.
Principal Nigel Brown (voiced by Lewis MacLeod) – A furry slug who is the principal of Elmore Junior High. Ever since he fell in love with Miss Simian, he has been a dangerously incompetent principal and spends most of his time flirting with her, thus keeping him from properly running the school. In season 2, his voice is a lot deeper.
Miss Lucy Simian (voiced by Sandra Searles Dickinson in Season One, Hugo Harrison in Season 2) – An elderly baboon who is Gumball and Darwin's sadistic teacher. She takes great pleasure in giving her students pop quizzes and being generally unpleasant. She is madly in love with Principal Brown, and he seems to gladly return the feeling. Miss Simian utterly despises Gumball and will do anything to ruin his mischievous plans. She has, however, been nice to Gumball at least once, with the real motive behind this being to win a teacher appreciation award, thus allowing her to complete her teacher trophy collection. One episode showed that Nicole was her student since preschool. In season 2 her voice is a little different, and she wears a pink dress instead of her grey with white polka-dots dress.
Rocky Robinson (voiced by Lewis MacLeod): An orange, fuzzy Muppet-like character who has various jobs around Elmore Junior High. Rocky is the son of Gaylord and Margaret Robinson, the Wattersons' next-door neighbors. He is good-natured and gets along with the kids and everyone else much better than he does with his parents.
Mr. Steve Small (voiced by Rupert Degas): A tall, fluffy creature who is the counselor of Elmore Junior High. He is interested in New Age culture and possesses hippie-like qualities in terms of appearance and behavior. Mr. Small's strange and unorthodox teaching methods are usually more confusing to the children than helpful, and most of the kids leave his office confused and not any better, if not worse from the time they entered. With this, many Elmore Junior High students are left wondering why he still has his job. Like other characters, Mr. Small is afraid of Tina Rex. He is also shown to have violent mood swings, which could possibly be attributed to bipolar disorder.
The librarian - The Librarian works at Elmore Junior High as the school librarian. She is a tree with yellow bark (skin) and turquoise leaves (hair). She also wears a turquoise dress and a very large pair of red rounded spectacles. As one of the elderly characters on the show, she has wrinkles along her face.
Josephine "Granny Jojo" Watterson (voiced by Sandra Dickinson) - The grandmother of Gumball, Darwin, and Anais, and the mother of Richard. Gumball has a strong fear of her due to his fear of getting kissed by her on the lips. She does not respect her grandchildren and calls Darwin "walking fish" and Gumball "the blue one". She told Anais to carry her heavy bags up to her room, which took her one day to accomplish. A flashback shows that even during Richard's childhood, she has maintained an elderly appearance. She uses extreme scare tactics to keep Richard and her grandchildren safe, so far as chasing Gumball down with a car to say he isn't safe outside, scaring Darwin while making a sandwich by cutting off her fake arm to say he isn't safe when there's a knife around and blowing up Anais's window to scare her from going outside. She speaks with a New York accent.
Gaylord and Margaret Robinson (voiced by Rupert Degas and Teresa Gallagher, respectively) – The Wattersons' stuck-up next door neighbors, and Rocky's parents. They are grey Muppet-like characters and they hate their neighbors with a passion. Gaylord is always grouchy and deeply despises Gumball for annoying him all the time; Gumball, however, idolizes him because he believes him to be a war veteran. Margaret is just as grouchy as her husband and is always in a bad mood. She never speaks; the only vocalizations she can make are hoarse whispers. While appearing to not have a good relationship, they actually enjoy arguing with each other. They drive a Cadillac Deville. They also argue every single day with each other.
Laurence "Larry" Needlemeyer (voiced by Rupert Degas) – A rock man who works at almost every movie/video game store, gas station, and grocery store in Elmore. Larry used to be known as "Lazy Larry", the laziest person in Elmore, until he lost his title to Richard during the summer of 1983. Larry ultimately despises the Watterson family, mostly because they are consistently getting him fired.
Doughnut Sheriff (voiced by Rupert Degas) – An ineffective doughnut police officer who works in Elmore. He is rather oblivious, and as such is not a very good police officer. Similar to Carrie, he is eternally hungry, because since he is a doughnut, anything he attempts to consume just goes out the other end of his mouth.
Sal Left Thumb (voiced by Rupert Degas) – A walking fingerprint who is a very dangerous criminal in Elmore. He often is seen doing some devious activity such as robbing a convenience store or trying to break into someone's car. Strangely, his weapon of choice is a rusty spoon, which, for some reason, many of the male characters in the show are terrified by. He has a New York accent and also has a habit of calling people "suckers." It is assumed that he is not as strong as he looks, considering he was knocked out when Nicole hit him with a frozen sausage.
Marvin Finklehimer (voiced by Dan Russell) – He is a red, elderly man in Elmore. He walks around with a brown cane and he wears an orange hat. He speaks in an old raspy voice. He is part of a group of elderly people that sit in front of a yard that Gumball seems to run into a lot. In the episode "The Watch", Darwin gives Marvin the watch over which The Wattersons and Marvin's family have feuded for several generations. At the end of the episode, Marvin and The Watersons fight over the watch to cash in the money it's worth.