Gumball (formerly Zach) Tristopher Watterson is the protagonist of The Amazing World of Gumball. He is a
Him in the show.
Originally, Gumball was meant to be a blue dog. Not much thought was put into this choice as it was more of a placeholder than a final design. As the creators developed the character further, they decided to make him a black cat in order fit the personality they had in mind for him: unlucky, but optimistic (black cats symbolize bad luck). The creators found this trait to be too restricting in terms of possible plots and stories. In addition, a silhouette cat would be "hard to read" on the backgrounds planned for the show. The decision was finally reached to have him blue, a decision that Bocquelet liked because blue isn't a color usually found on cats, and it had a "70's-80's Japanese mascot" sort of feel.
In the actual show, Gumball is a light blue cat. On his oversized head, he has six whiskers, but only five are visible most of the time, because his head is mostly shown at an angle. He usually wears grey trousers, coupled with a tan sweater, which has brown cuffs and a brown collar. Like his mother and father, Gumball doesn't wear shoes, and is the only member of the Wattersons without visible eyelashes, although, in some episodes, he is seen with visible eyelashes, like in "The Refund" and "The Boss." The inside of his mouth is pink, his tongue is light pink, and his nose is orange.
In Season 2, his design changes slightly. His head and his whiskers are bigger, while his eyes and tooth are rounder.
In Season 3, Gumball's eyes are permanently round along with the rest of the Wattersons.
Gumball is a very imaginative person. Despite his mediocre academic performance, he can be surprisingly brilliant when it comes to formulating all sorts of mischievous schemes. This side of him can be seen in episodes such as "The Plan," in which he quickly formulates a basic outline to he and his siblings plan to "save" their mother, and in "The Scam," in which he forms a crafty scheme that will allow him to cleanly heist the town's candy effortlessly. Such a side may also suggest Gumball is smarter than he lets on, as hinted by his expansive vocabulary, cooking skills, and ukulele skills as well.
Gumball is also pretty optimistic. Despite his cynicism towards society itself, as seen in episodes such as "The Bumpkin" and "The Money," he is still fairly positive in what to expect out of people (though there are exceptions). When his family is financially suffering in "The Money," he's quick to tell them of the joys of family and pushes them to be more optimistic. In "The Others," he's quick to reject Clare's notion of "no happy ending," only wanting to see her have a happy ending (no matter how forced it was). He's also happy to help others, as seen in "The Void," "The Upgrade," and "The Slide," in which in all three he went great lengths to assist Molly, Bobert, and Rocky, respectively.
In general, Gumball is very protective of his loved ones. On multiple occasions, he's quick to go into a sort of "over-protective" mode whenever anybody tries to hurt his siblings, Darwin and Anais, as seen in "The Parasite," in which he tried to nearly poison Jodie when she thought she was hurting Anais, or in "The Rerun,"in which he aimlessly tried to attack Rob out of rage when Darwin died.
Despite him being a good and positive person on the inside, Gumball is very snarky and sarcastic towards people who aren't his family or his girlfriend, Penny (and even then, he can be an allack towards his siblings at times). He's quick to diffuse all sorts of quips towards others, ranging from fairly harmless to sometimes blunt and rude. As demonstrated in episodes such as "The Stories" and "The Test," these snarky comments are impulsive and sometimes, he can't help it.
Gumball also has a fairly massive ego, which seems to be a fault of his. When it's not tamed properly, his ego can drive him to do some pretty jerky things. Darwin tapping into his musical talents in "The Triangle" caused Gumball to have short-lived jealousy towards him before he realized he was wrong. His ego also explains his relationship with Alan; the fact that Alan is so effortlessly loved drives Gumball to expose him for being scummier than he lets on (which is later turns out to be accurate.). This ego also makes him very sensitive, as seen in "The Meddler," in which he's an emotional wreck when he's told his cheerleading performance was terrible.