Darwin Watterson is the deuteragonist in The Amazing World of Gumball. He used to be Gumball's pet goldfish, but, one day, he grew legs and generally adapted to life outside of water, so he was adopted by the Watterson family.
Darwin is an orange goldfish with arms and legs. His goldfish-shaped head takes up his entire body, with his fins and legs hanging down from it. He has retained his goldfish tail and fins, the latter of which he now uses as arms and hands. His legs are much longer than his body, ending with plain feet matching the color and texture of the rest of his body. Usually, though, he covers them with green and white sneakers. Darwin is also shown to have a bubbly butt on the back of his head, as revealed in the official trailer. A common misconception in Season 1 was that he also wore a black shirt, as well as pants, but, that was actually just a shadow cast by his big head. The inside of Darwin's mouth is red, and his tongue is orange-red.
Darwin apparently has thick coatings of blubber, making him resistant to massive pain, as he is shown unharmed in "The Responsible," after a painful face-first slap on a concrete sidewalk from way up in the air. The blubber's depth is about the length of Gumball's arm, as shown in "The DVD," where Gumball had to sink his whole arm into Darwin's head just to reach his cheekbone. Darwin also thinks he has perfect skin as shown in "The DVD." Whenever Darwin's feet are bare, they are often pixelated, as in "The Meddler." However, sometimes they are not pixelated, as shown in "The Club," when he is swimming, in "The Goons," when he is toe wrestling Richard, and in "The Dream," when they end up in the mall without having his shoes on. In "The Dream," he says that he considers his feet worthy of a censor, because, it is the only place he wears clothes.
In Season 2, Darwin gets a redesign. His black shadow is more transparent, almost to the point where it's not noticeable. Also, his legs get slightly fatter, and he loses one eyelash on each eye (two on each eye instead of three). Like Gumball, his eyes are more round. His voice also started to sound slightly deeper, and whenever he screams, his voice squeaks, probably due to Kwesi Boakye, his voice actor, entering puberty.
In Season 3, Darwin's eyes are permanently round along with the rest of his family.
Darwin is a very happy and positive person. He always tries to see the best in most of the scenarios he's in, and in general, always tries to have a smile on his face. Not only does he desire to be happy, but he also desires to see others happy. His selfless acts of happiness can be seen in episodes such as "The Fan," "The Advice," and "The Stories.". In all three episodes, he chooses to do the things he does in order to make a particular sad person happier.
Darwin is also a very grateful person, as seen in "The Flower" and "The Night;" both episodes show Darwin not wanting much and just being happy with his current life.
Darwin also very optimistic; he expects the best in people, and he has a romantic and somewhat naive view on the world. His idealistic and naive viewpoints can be seen in "The Wicked", in which despite his brother's views and Mrs. Robinson's obvious malicious intent, he firmly believes that Mrs. Robinson is a good person at heart, and that there is a reason for her actions.
Darwin has a strong sense of honestly; he also desires to tell the truth, no matter how much trouble it may cause. His strong sense of honesty can be seen in "The Shell" and "The Gift," in which he can't adhere to the simplest of Gumball's white lies. His honesty can also be seen in "The Words", in which his brutal honesty is a source of conflict for the episode.
Darwin is also morally grounded in general; he's typically the one to stop his siblings from doing anything wrong, and he is slow to take "shady" approaches. Darwin's reluctness to do anything wrong can be seen in "The DVD," in which he tells Gumball not to pirate Alligators on a Train, opting for a more honest and cleaner route. This trait of Darwin is what causes Gumball to see him as a "moral guardian" as evidenced in "The Sidekick."
Darwin is also very sensitive and empathetic. He is very affectionate of others, as seen in his interactions with his family, and specifically, Gumball, throughout the series. This love and affection may be a weakness of his, however, as a result, he is very possessive without his loved ones, and feels very lonely when not around them. Such is evidenced in "The Bros" and "The Burden", in which Penny's newfound relationship with Gumball makes him jealous, and presumably for the first time in his life, as suggested by the events of "The Flower."
Despite Darwin's general happiness and positivity, he has been known to get angry at times when pushed beyond his limit. Although it's a side not often seen, "The Banana" and "The Words" both display what can occur when Darwin is angry. He can resort to senseless violence when given a reason to do so.
Voice Actors Edit
- Kwesi Boakye (US/UK/AUS/CAN) (Seasons 1-2, and most of "The Kids")
- Terrell Ransom, Jr. (US/UK/AUS/CAN) (the climax of "The Kids," the rest of Season 3-"The Copycats")
- Donielle T. Hansley Jr. (US/UK/AU/CAN) ("The Copycats"-present)
- Yumiko Kobayashi (Japan)
- Andrea Di Maggio (Italy)
- Iván Sánchez (Spain)
- Ghadi Hakeem (Middle East, Seasons 1 and 2 until "The Lesson")
- Yousuf Jalal Shallal (Middle East, Season 2 starting with "The Game - The Finale")
- Richard Yenni (Middle East, most of "The Kids")
- Fares Smerat (Middle East, Season 3)
- Bergen Coşkun (Turkey)
- Yago Machado (Brazil)
- Sacha Capelluto (France, Season 1)
- Tim Belasri (France, Season 2-present)
- Gerardo Mendoza (Latin America)
- Noah Nikolaisen (Norway)
- Jang Eun-suk (South Korea)
- Nathan van der Horst (Netherlands)
- Egill Scheving (Iceland)
- Darwin is the only Watterson who doesn't wear pants.
- Darwin can regrow his legs, as shown in "The Kids."
- According to an interview with Ben Bocquelet, Darwin was originally designed for a show where mythical animals hid in a child's backyard. When the show wasn't produced, he added Darwin to the show, because he liked his design. 
- Darwin has a major crush on Carrie, as seen in "Halloween," "The Oracle," and "The Scam."
- In "The Oracle," he appears to be embarrassed about it.
- Darwin seems to be multilingual, as he spoke a complex Chinese sentence in "The DVD," and spoke French in "The Treasure," though the latter may only have been a temporary ability gained through hypnosis, and the subtitles for the former only stated "No."
- Darwin is also capable of speaking with non-anthropomorphic animals, as seen in "The Question," "The Traitor," and "The Origins: Part Two."
- Darwin can breathe in both water and air.
- In Project Exonaut, Darwin is available as an exosuit for 1,000 coins.
- In "The Dress," we see that he uses his left hand when he's drawing Gumball in the dress. However, he does other common tasks with his right hand. This suggests that he may be ambidextrous. It might be a development oversight as well.
- On an exclusive video on the official "Elmore Stream-It" YouTube page, it is revealed that Darwin can exhale for much longer than Gumball can.
- Darwin most likely has the longest name out of any character. He has seven names, as shown in "The Party."
- Darwin's name is most likely based on the scientist Charles Darwin, who gained fame for his theory of evolution. A fish with legs or a "Darwin fish" is also considered somewhat of a universal symbol for Darwinism.
- "Raglan" may refer to the HMS Raglan, a World War I Royal Navy monitor vessel. The name may also be a reference to the township of Raglan, New Zealand. The town is well known for its surfing, as well as a rare subspecies of dolphin. Darwin has been shown to have the ability to make dolphin sounds.
- "Caspian" is likely a reference to the Caspian Sea, the world's largest enclosed body of water. Prince Caspian is a character in C.S. Lewis' Chronicles of Narnia series. Darwin and the prince both possess many similar traits, and Prince Caspian rode through the sea on a ship called The Dawn Treader.
- Ahab, another of Darwin's middle names, is a reference to Captain Ahab, a sea captain obsessed with killing the white whale Moby-Dick in the book of the same name.
- "Poseidon" is a reference to Poseidon (known as Neptune in Roman mythology), the god of the seas from Greek mythology. Poseidon is also the god of horses, and Darwin is shown to be used by Gumball as a mount on more than one occasion.
- Nicodemus the Hagiorite was a saint who lived from 1749-1809. He was purported to possess a love for all things, much like Darwin's seemingly constant outlook on life. Nicodemus was also in the Bible, being 'reborn' as a Christian. This parallels Darwin's transformation from ordinary fish to a "reverse mermaid."
- Darwin has a habit of standing in his seat as opposed to sitting down, especially in Season 1.
- Darwin was originally a CGI animated character, but this was changed later on because of the difficulties of having a major character animated in this fashion.
- In "The Party," Darwin claims to be part suckerfish.
- Darwin is quite athletic. He can run as fast as both Anais and Gumball, as shown in "The Quest," "The Kiss," and "The Remote," can climb faster than Gumball, and is a skilled swimmer.
- In "The Words," it is revealed he's bald, although in "The Refund," it is shown that he can grow leg hair, as well as scalp hair in "The Voice."
- In "The Bet," it is revealed that it took Darwin five years to learn facial expressions, and he still has some trouble recognizing them.
- Darwin, along with Evil Turtle, is the only Watterson that isn't a mammal of some sort.
- The events of "The Origins" and "The Origins: Part Two" reveal that Darwin was given to Gumball because he needed a new pet fish to replace the dead ones.
- In "The Game," it is revealed that he is the third of the several fishes named "Darwin" that the Wattersons have owned, hence his name.
- In "The Internet," Darwin is shown to be good at playing the ukulele.
- In "The Dress," Darwin draws Gumball really well. This could mean Darwin is an expert artist. However in "The Mustache" and "The Procrastinators," his drawings somewhat resembles a four-year old's drawing.
- According to the episode "Halloween," Darwin has samhainophobia, a fear of Halloween.
- According to an interview, Darwin was inspired by Ben Bocquelet's childhood friend, Paul. 
- As revealed in "The Castle" and "The Flakers," Darwin is able to scream at an extremely high-pitched volume. It is so high that it can break the glasses from all the houses of a block.
- In "The Recipe," it is revealed that Darwin believes people are born on cabbage patches.
- Darwin is affectionate, he likes being kissed, as seen in "The Kiss," holding hands (Gumball mimics him saying so in “The Sidekick”) and hugs, as he states in “The Hero."
- In "The Void," Darwin's design from the early reel can be seen in the background of the Void.
- In the episode "The Allergy," it is suspected that Darwin is allergic to stupidity, but it is later revealed that actually he is allergic to feathers.
- In "The Burden," it is revealed that Darwin is possessive and fears being lonely.
- Also, in the same episode, it is implied that he had previous families when he "talks" to Chris Morris about him not being one of his dads and when he mentions Gumball being his "brother from another mother" in "The Bros."
- Darwin likes Mexican food, as indicated in "The Countdown" (when he asks Gumball not to "diss" it because it "rocks").
- As of yet, "The Apprentice" and "The Awkwardness" are the only two episodes that he does not appear in.