Gilligan (played by Bob Denver) - The title character of the show. Gilligan is a crewman of the S. S. Minnow who worked for the Skipper. He is a bumbling idiot who always seems to mess up the castaways' escape. He wears a red shirt, light blue pants, and a white sailor's hat. In the never-aired pilot episode, it is revealed that his first name is Willy.
The Skipper (played by Alan Hale, Jr.) - His real name is Jonas Grumby and he is the captain of the S. S. Minnow. He is well over-weight, leading to numerous fat jokes from Gilligan. Such an instance is when the Professor and Gilligan are helping him into a wetsuit: the Skipper says that he just has big bones, to which Gilligan adds: "and they're covered in big meat." Whenever he gets frustrated with Gilligan, he swats him in the head with his hat.
Thurston Howell, III (played by Jim Backus) - Thurston is a millionaire used to luxurious living and never does any work on the island. The only exception is when the castaways believed that Mr. Howell was broke and making him do work. He always devises get-rich-quick schemes on the island. Thurston was originally a multi-billionaire until the stock market crash rendered him a multi-millionaire.
Mrs. Howell (played by Natalie Schafer) - Thurston's wife. She can be more spoiled than Mr. Howell at times, but is always the first to want to try something first. Mr. Howell always calls her "Lovey." Her name is Eunice Wentworth Howell.
Ginger Grant (played by Tina Louise) - A movie star from Hollywood. Ginger usually tries to use tricks from the movies she starred in to solve problems causing other castaways to rescue her from any dangers that befall her. She helps Mary Ann with cooking and dishwashing.
Professor (played by Russell Johnson): His real name is Roy Hinkley and he was a high school teacher before being stranded on the island. He has numerous scientific degrees, and using his knowledge built many things on the island out of bamboo and other materials. He is the most well-learned of the group and always has a logical answer to everything (although not always correct).
Mary Ann Summers (played by Dawn Wells) - A farm girl from Winfield, Kansas. Not much is said about her before getting to the island. She is portrayed as a typical "girl next door" and does most of the laundry and cooking with some help from Ginger. She is famous for her coconut cream pies which usually end up on Gilligan's face.
Radio Announcer (voiced by Charles Maxwell) - An announcer on the radio that the castaways own. The castaways would listen to his plot-advancing radio bulletins in many episodes and always with perfect timing to hear the exact news they needed to know.
Wrongway Feldman (played by Hans Conried) - A fighter pilot from World War I. He was stuck on the island when he tried to fly around the world in the spirit of the Bronx. He leaves at the end of the episode, but returns later saying he will stay on the island. He leaves again however, but he crashes and never appears again. The castaways get a message from him saying he "crashed on a strange island" which appears to be Hawaii.
Dr. Balinkoff (played by Vito Scotti) - A mad scientist who appears twice. For his first appearance, he takes the castaways to his secret lair on another island. In the end, the castaways escape. The second time, he uses mind-control rings to get the castaways to rob Fort Knox. He then flees when they attack him with coconuts and is never seen by them again. He owns a pet monkey named Igo
Japanese Sailor (played by Vito Scotti) - Appeared in two episodes. For his first appearance, he locks everybody on the island up except Gilligan and Skipper. In his second appearance, he appears in a flashback of events that never happened.
The Gorilla (played by Janos Prohaska) - The only animal who acts as an antagonist on the island that causes mayhem and mischief among the castaways. In the episode "Diamonds Are an Ape's Best Friend," he kidnaps Mrs. Howell because her perfume acted as a pheromone. In the episode "Chain of Command", he disciplines Gilligan to be a better leader. In the episode "Forward March," he shells the castaways with hand grenades after he has found a stash of WWII weapons in a cave. In the episode "Our Vines Have Tender Apes," the Gorilla is replaced by an Orangutan.
In some episodes, there are different people who appear on Gilligan's Island that are either visitors or have been on the unexplored parts of the island.
The Mosquitoes - A rock/pop group who came to the island to escape all their fans. They were annoyed into leaving by the castaways, who eventually got them to leave by the girls forming the musical group "The Honeybees." The Mosquitoes left, leaving behind one of their records, called "The Mosquitoes at Carnegie Hall". Their names are Bingo, Bango, Bongo, and Irving.
Erika Tiffany-Smith (played by Zsa Zsa Gabor) - Appeared in the season two episode "Erika Tiffany-Smith to the Rescue". Erika is a rich socialite and is a rival to Mrs. Howell. However, Mr. Howell takes a liking to Erika when she lets word out that she wants to buy the island; and, as usual, Mr. Howell takes all money offers. Erika falls in love with the Professor, ignores Mary Ann's sweetness and the Skipper's advances of romance, and treats Gilligan (like everyone else) as a butler. Ginger adores Erika because of her owning several movie studios; however, Ginger doesn't appear on screen with Erika at all. Erika leaves claiming to return and rescue the castaways and buy the island. Like other visitors, she never returns. She's heard on the radio at the end of the episode saying she doesn't know the coordinates of the island.