These are the relationships Gumball has with the other characters in the series.
Darwin is Gumball's adopted brother and his fully-fledged friend. The two are often seen together, and thus, are prone into getting into mischief with each other. Through thick and thin, the two seem to have each other's back.
Gumball's love for Darwin is what allowed Darwin to be the way he is in the first place. "The Origins," part one and part two, gives more insight into the strength of the two brothers' bond. Gumball's love for Darwin is so strong that it allowed Darwin to quickly evolve and return home to the family.
Gumball describes Darwin as a sort of "moral" guardian to him, for Darwin is the one usually to call out his brother when his plans cross into immoral territory. As seen in "The Sidekick," Gumball sees Darwin in a better light than he lets on.
Despite this, Gumball is known to occasionally retaliate again, specifically when it involves Darwin achieving more than he does. Such is the case in "The Triangle," in which Darwin discovers his secret talent for the swanee whistle and gets a part in the school band. This prompts Gumball to impede his brother's progress as much as possible.
Gumball loves his little sister very much and sometimes appears to be very proud of her. Despite his occasional snarkiness towards her, Gumball does truly care for her.
Anais can often act as a counter-balance to Gumball's tomfoolery. In episodes such as "The Plan" and "The Lie," Anais is quick to point out all the flaws in Gumball's brash actions. In "The Plan," Darwin also plays that role with her, making for a double wham.
Gumball is also very protective of his little sister. In "The Pest," Gumball is quick to get into a duel with Billy after he catches him insulting her. Gumball also tries to poison Jodie in "The Parasite" when he believes that Jodie is abusing Anais' social awkwardness.
Gumball loves his mother very much and looks up to her. Despite this, Gumball often fears his mother's temper, as seen in episodes such as "The Fridge," in which he comments how her scary temper and desire to win has teared the family apart.
That aside, Gumball does legitimately hold his mother up in high regard. In "The Mothers," both he and Darwin are eager to prove to their friends that their mother is the best. In "The Fury," he is blown away by his mother's abilities.
Nicole also genuinely desires to be closer to his son. In "The Meddler," she takes time out of her work to give her sons the attention they desire, and in "The Shell," she goes out of her way to comfort Gumball when he fears he may have lost Penny forever.
Richard is Gumball's father, but Gumball sees Richard more as an older brother rather than an actual father figure. Gumball often plays video games with his father, and in general, he can be seen goofing on with his children as opposed to showing any parental authority. As shown in "The Password," however, Richard can exercise some authority, specifically when Gumball and his brother pushed him to his limit.
Because of this, Gumball fails to take his father seriously. This can be seen in "The Hero," in which he insults his father, believing him to be a joke. This is rectified by the end of the episode, as Gumball rebonds with his father.
It's shown that earlier in Gumball's life, such as 'The Hero," "The Origins" and "The Choices," Richard was very much an active parent in Gumball's life; he always had his eye on him and did everything in his power to be the best father possible.
Granny Jojo is a very overprotective grandmother towards Gumball and his siblings. In "The Authority," she takes over Nicole's job as caretaker of the house, and in her new position, she scares Gumball and his siblings straight. Despite this extreme method to parenting, Granny Jojo only has the best intentions for Gumball. In "The Man," Gumball agrees to help Granny Jojo reunite with Louie despite such actions being against his father's wishes. He is also very supportive of the marriage between Louie and her.
Even though Louie is a fairly recent addition to the Watterson family, he still loves Gumball and his siblings as if they were his biological grandchildren.
In "The Man," Gumball was very supportive of Louie's relationship with Granny Jojo, wanting both parties to be happy despite his father's obvious disdain.
When he is later married to Granny Jojo and becomes the Watterson children's step-grandfather, Louie gives a gift of $50 (that the children initially believed to be $5000) as gift for "being his favorite grandchildren."
Gumball and Penny had always had a mutual crush on one another. Before the big confession, both Gumball and Penny were shy and awkward with each other. Both seemed to be especially introverted when speaking with each other. This is until "The Shell," when Gumball finally admits his true feelings to Penny and kisses her on the lips. Penny reciprocates their kiss and they began their special relationship forth onwards.
In "The Shell," Gumball helps Penny get over her insecurities when she comes out of her shell. He's there to tell her how her appearance doesn't matter, and that he will always love her. After that, Gumball and Penny seem to share a healthy romantic relationship, often spending time together as seen in "The Blame" and "The Misunderstandings." Gumball also occasionally likes to shake things up, as seen in his romantic quest in "The Romantic."
Gumball's and Penny's trust in each other is strong that when Gumball accidentally kisses Sarah in "The Disaster," Penny trusts Gumball that it wasn't on purpose, but instead she gets upset over the language change.
Carrie and Gumball are close friends. Although Carrie initially took advantage of the friendship, as seen in "The Ghost," in which she possess Gumball's body for a junk food spree, the two later become good friends. In episodes such as "Halloween" and "The Flower," Carrie is quick to goof off with Gumball and his brother. "The Scam" also further highlights the mischievous side the two share.
In the episode "The Mirror" she came to Gumball's aid when he was cursed by the Snatcher, who is her long lost father, and Gumball also helped to reunite her with her father. In "Halloween," when Gumball, Darwin, and Anais get sucked into the underworld, Carrie seems sad and distraught.
Gumball and Bobert appear to be greatly friendly between one another despite. In "The Bet," Gumball and Darwin feel sorry for Bobert having no one to play with, so they include him in one of their games.
In "The Upgrade," Gumball and Darwin convinced him to upgrade into a new version. During the same episode, he also expressed his feeling of replacing him with the New Bobert, but remarked at the end that he likes Bobert as he is. In "The Loophole," Gumball and Darwin grow concerned about the potential danger he poses on everyone around him and set up a few rules to prevent him from hurting anyone.
Despite the age gap, Rocky finds a good friend in Gumball Watterson. In "The Boss," Gumball and Darwin help Rocky land an office job so that he may gain the respect of his father.
As seen in "The Slide," Darwin, Gumball, and Rocky are all gaming buddies, often playing an online MMORPG together; in that same episode, Gumball helps Rocky find his true love.
Although Banana Joe was initially unfriendly towards Gumball, as the series progressed, the two soon began to befriend each other, and as a result, Gumball is now one of Banana Joe's closer friends. Such is the case in "The Banana," in which Banana Joe is temporarily upset with Gumball and Darwin because of a misunderstanding with a pen.
In "The Mothers," Banana Joe agrees to participate in Gumball's and Darwin's arranged "Mom-Off." In the "The Misunderstandings," Banana Joe tries to join Gumball, but because of the urgency of the situation Gumball respectfully declines Banana Joe's offer.
Gumball and Idaho are on decent terms with each other, and seem to share a decent friendship. In "The Bumpkin," Idaho tags along with Gumball to his house so that Idaho may teach Gumball how to live a "clean" lifestyle. Although their initial disdain, Idaho managed to get all of Gumball's family aboard the concept of living a clean lifestyle.
Later that night, Gumball decides to teach Idaho the fun of "the party life"; even after Idaho nearly dies of such a lifestyle, Gumball and Idaho still manage to remain on decent terms.
Because he is very protective of his daughter Penny, Patrick used to view Gumball with suspicion. He first meets Gumball in "The Date," and initially views him with disdain. Patrick once more keeps a wary eye on Gumball in "The Knights," where he now seems to be aware of Gumball's crush on Penny. Patrick's apprehensive attitude towards Gumball only ends in "The Shell," in which he unintentionally insults his daughter, who has broken out of her shell. Gumball finally stands up to Patrick and calls him out on his actions. In the end, Patrick approves of Gumball and Penny's relationship, with continuity prevailing over the status quo.
Mr. Robinson is somewhat an idol to both Gumball and his companion Darwin, but mostly to Gumball. He always tries to earn his favor, most of the time failing at it such as in "The Debt" and sometimes actually being successful to convince him like in "The Car," though only for a very minuscule time span. Ironically, Mr. Robinson despises Gumball for irritating him all the time. Though most of time Mr. Robinson despises Gumball's presence, a moment in "The Debt" actually resulted in Mr. Robinson thanking Gumball for saving his life, but still yells at him for ruining his great performance.
Gumball and Tobias have a history of rivalry behind them, although their relationship is somewhat unclear. He tends to be jealous of Gumball at times, expressed in "The Voice," where he is furious that he isn't the "main character" in his own story, and he should be the one on cool adventures and in "The Knights," it is shown that he has a crush on Penny as well but she only has feelings for Gumball. Also, in "The Third," Tobias becomes Gumball and Darwin's friend for twenty dollars, but he ends up ignoring Gumball and befriending Darwin.
They may be on somewhat-decent terms as Gumball allowed Tobias his own segment on his home movie in "The Tape." Also, in"The Slap," Gumball felt left out when Tobias doesn't slap him with his special high-five slap. He tried his best to make Tobias slap him on the butt but failed.
Throughout Season 1, Tina bullied Gumball on occasions like in "The Mustache," pelting him with dodge balls and even one bowling ball, and in "The Meddler," insulting him for how he looks with his mum with him at school holding his hand. In "The Fight," it appeared to be that Tina had been bullying Gumball and had challenged him to a fight, but in the end, she explains that the physical abuse she had inflicted on him was her idea of having fun with him (it is presumably her natural instincts as a T-Rex that make her think this way), and so, she had actually always thought of Gumball as her friend.
Since their resolution in "The Fight," Gumball and Tina had been considered former enemies, but there have still been instances of conflict between the two, like in "The Flakers" where Gumball told Tina that she couldn't make it as a pianist because she only has 4 fingers only to be honest, which upset her greatly regardless and her retaliation was to stomp him if he didn't take it back.
Gumball disapproves of Clayton's compulsive lying, but likes him enough to want to give him a chance to quit as followed in "The Skull," in which Clayton also states he thinks Gumball is really cool and really just wanted to impress him. This is explored further in "The Move," where one hard to believe thing Clayton told him turned out to actually be true, about a martial arts move which temporarily paralyzes.
Sarah has a crush on Gumball as shown in "The Comic," though he does not reciprocate her feelings. Although he is generally on friendly terms with her, he does find her irritating as a result of her stalking, as seen in "The Fan."
In "The Fan," even though Gumball is pretty upset with the fact Sarah has been stalking him for years, he still decides to act out her erotic fanfiction as an act of friendship. Gumball also takes part in the "LaserHeart" universe that Sarah created in "The Comic."
Although Alan has nothing against Gumball, Gumball finds him very irritating due to his flawlessness and nobility. In "The Saint," Alan's saintly behavior got Gumball on his nerves and he decides to break Alan down to his level. But no matter what Gumball did, Alan remained the same. Even though he can't stand his personality, Gumball does try to make up for it in "The Traitor," only for him succumb back to his former disdain for him.
Back in Seasons 1 and 2, Rob used to be friendly towards Gumball. However, due to the tragic incident that happened in "The Void," he swore revenge on Gumball and Darwin.
In "The Bus," Rob became more focused on defeating Gumball than Darwin. His evil plan was to blow everybody up in the hijacked school bus with an explosive suitcase, but his plan was foiled and got arrested by the police for his crimes.
In "The Disaster," he purchased the Universal Remote from the Magic Van, giving him new powers to control the universe. He was responsible for ruining Gumball's life by taking away his family and nearly killing his girlfriend, Penny. Gumball confronts his nemesis in a battle, but Rob defeats him by banishing him to the Void, but Gumball was able to save himself by rewinding himself back to the beginning of the disastrous day.
In "The Rerun," after saving Rob, Gumball tries to befriend him, but the circumstances makes their friendship short-lived as Rob has to rewind back to the beginning of the day.
In "The Ex," Rob makes Banana Joe his nemesis instead of Gumball, making him sad. Gumball later tries to become friends with him, but inadvertently saves Banana Joe from his trap, causing him to snap, saying that he is the most insufferable, annoying, selfish person that he had ever met, making Gumball happy.