- Zach "Gumball" Waterson is the main character and protagonist of The Amazing World of Gumball. He is a twelve-thirteen-year-old, light blue boy cat with whiskers and goes to 7th Grade at Elmore Junior High with his ten-year-old adopted little brother and best friend Darwin and his four-year-old sister Anais. Gumball is in Miss Simain's class. Gumball also had a crush on Penny and has a crush on Carmen (Alan's former girlfriend), who is also in Miss Simian's class. Penny and Masami had and Carmen has a crush on Gumball as well, but they struggle to express their emotions to each other. Gumball loves Darwin (sometimes formerly), Penny (formerly), and Anais.
Gumball is a light blue cat. On his oversized head, he has six whiskers but most of the time only five are visible because his head is always shown at an angle. He usually wears grey trousers coupled with a tan sweater which with brown cuffs and a brown collar and jeans. Like his mother and father, Gumball doesn't wear shoes, has the hi-top (that he likes) wallpaper in his room and is the only member of the Watterson family invisible eyelashes. He's sometimes gross, crazy, weird, evil, a "rebellious streak" boy and bully.
Gumball is portrayed as a fun-loving, imaginative, optimistic, and a very mischievous cat. When his mishaps get himself into a mess, he usually attempts to fix things with somewhat dimwitted ideas, which usually get him into even more trouble than before. No matter how his schemes resolve themselves, Gumball's naivete stops him from learning his lesson. He usually plans his mishaps with Darwin. Like Darwin, Gumball does not appear to notice deception, which may mean that he is too optimistic to notice most negative things around him.
Gumball has a big ego and it is where he is most sensitive, though otherwise he is usually positive on all matters concerning him. Gumball is smart, but that doesn't mean he's wise. For instance, at times he acts really stupid and goes to great illogical lengths to find something; however, he has shown some degree of cleverness in other instances. His antics have gotten him in dangerous and often life-threatening situations, usually saved by luck someone more sensible at the time.
He is a decent cook, making a very good sandwich for Darwin as mentioned in The Secret, and is shown making a good (albeit spicy) meal for him in the same episode. However, in The Responsible, Gumball makes disgusting food for Anais, consisting of a rotten fish between bread slices and an old shoe.
Even though Darwin who's sometimes bad is adopted, Gumball shares a genuine sibling connection with Darwin. The two boys have a big imagination and like to get into mischief. They get along very well, although they argue at times. However, Gumball can be a bad influence on Darwin. Gumball sometimes turns his nose up at Darwin's ideas and they both go for a more childish or foolish approach.
Gumball usually relies on Anais with his problems. She likes to inform Gumball that she is right and he is wrong. Although Gumball will never admit it, he actually loves and admires his sister and knows that she is right about things most of the time.
Gumball hates his mother who's sometimes bad having a fur-trigger temper very much, though he does believe she is terrifying. He does not like to admit to wrongdoings to his mother because of Nicole's fiery fur-trigger temper.
Gumball loves his father very much and inherits his silliness from him. However, Richard can be tough on Gumball when the situation demands it and completely aloof otherwise. He's also been known to make fun of him sometimes and use their foolishness to his advantage. As seen on an Elmore Stream video, Gumball likes to poke Richard's "weird bit on his belly" when he is unaware of it. He sometimes had the fur-trigger temper.
Penny is Gumball's former love interest. Gumball has a former gigantic crush on her, and Penny has one on him as well. He often blurted out professions of love and got away with it either by keeping it as a secret, hiding it, twisting it, or hoping she ignores it. Despite it being somewhat obvious that Penny liked him back, he is always nervous when it comes to potentially romantic events because he is afraid that she might reject him. When they are about to kiss, the moment is usually interrupted. In the episodes "The Party" and "The Meddler" (2011-2012), Gumball said he doesn't love Penny.
Gumball idolizes Mr. Robinson the sometimes bad man and always tries to earn his favor. Ironically, Mr. Robinson despises Gumball for irritating him all the time. Although, in The Debt, Mr. Robinson does thank Gumball for saving his life, but then yells at him for ruining his great performance.
Gumball and Tobias (bully of Gumball) have a history of rivalry behind them, although their relationship is somewhat unclear. In The Pressure, Tobias and Gumball form a no-girls pact and Gumball doesn't uphold it very well. Also, in The Third, Tobias becomes Gumball and Darwin's friend for twenty dollars, but he ends up ignoring Gumball and befriending Darwin. Pure Aggression looks exactly like jealosy but he has almost infinite strength.
- Logan Grove (voice) and Katy Perry/Calvin Harris (sing) (US/UK/EU/Canada)
- Kumiko Higa (Japan)
- Bernard de Mory (France)
- Federico Bebi (voice) and Leonardo Caneva (sing) (Italy)
- José Antonio Toledano (Mexico/Latin America)
- Rebekka Weissfeld (Danish)
- Gumball sometimes exhibits more naturalistic cat behaviors such as moving his ears and tail, meowing, and retracting his claws.
- Gumball's sweater was revealed to have been found by his dad in a sewage outlet in The Date .
- Gumball is shown to have some health issues. In The Club , it is shown that Gumball has a weak bladder.
- Gumball is terrible at catching things, as shown in The Quest.
- Gumball hates watching the shopping channel, as shown in The Laziest .
- Gumball has been shown to be a horrible liar on numerous occasions.
- Although Gumball has six whiskers, only five of them are visible because of the angle of his head. In The Poltergeist when Gumball does the joke of a pea on a fork you can see that he has 6 whiskers.
- He has very wide hips, which is unusual because this feature is more commonly known on female characters in animation.
- Both Gumball and Anais placed 4th in The Dumbest since they both forfeited at the same time.
- In The Club, Nicole reveals that she and Richard agreed to give Gumball the middle name "Christopher", but Richard confused it for "Tristopher" on Gumball's birth certificate. His middle name was also confirmed as "Tristopher" on James Lamont's Formspring.
- Gumball has arachnophobia, which is a strong fear of spiders, as shown in The Date.
- In The Fight, it's revealed that Tina the bully dinosaur actually thought of herself as Gumball's friend.
- It is revealed in The Date that Gumball plays the clarinet.
- In the other episode, Gumball and the librarian (voiced by Tersea Gallagher) said shut up to other people, the theif and Mr. Small when other people, the theif and Mr. Small stole his house.
- Gumball acts like Gavin Sheilds (who was born in August 1999).
- Gumball looks like Rachel.
- Gumball was 12 years old in episode 1 and is 13 years old in episode 2.
- In The Name, Gumball's real name is revealed to be Zach. He later changed his real name to Gumball.