Darwin Raglan Caspian Ahab Poseidon Nicodemius Watterson III better known as just Darwin, is the deuteragonist in The Amazing World of Gumball. He used to be Gumball's pet goldfish, but, one day, he grew legs, gained the ability to speak, and generally adapted to life outside of water, so he was adopted by the Watterson family.
Darwin is a 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, this is probably because of Kwesi Boakye, his voice actor, entering puberty.
In Season 3, Darwin's eyes are permanently round along with the rest of his family.
Due to his sudden entrance into the world, his perspective of it is somewhat skewed and naïve. He has trouble understanding many situations. Often people have to point out his misconceptions and faults, such as the time he didn't know the definition of dates, and when he used a DVD as a pizza cutter.
Darwin is an overall happy person, sharing his best friend Gumball's optimistic view of life. His cheery personality shows in several episodes, most notably in "The Flower," where he was immune to the effects of Jealousy, due to being completely satisfied with his life. However, his jealousy is triggered when Gumball and Penny start dating, as seen in "The Burden" and "The Bros," causing him to go desperate lengths to break Gumball and Penny up in the latter. It takes a lot to trigger a negative reaction from him, but when provoked far enough, he can get very intense. A good example is in "The Banana," where he trashed Banana Joe's locker, and threatened grievous bodily harm to him, all in retaliation for his pen being chewed, and his homework getting ripped. Incentives also seem to fuel him up, like in "The Fridge," where he repeatedly smashed a ball into Gumball's face, all for the sake of a top spot on the fridge.
Darwin's happiness may just be a façade, though, as in "The Words," it is shown that people actually annoy him a lot; he just hesitates to tell them off. With help from Gumball, though, he begins telling people, often with intense hostility, everything he hates about them. Another example is in "The Limit"; when Darwin, Gumball and Anais were all sulking, and upset over having their day wasted going to the mall without any treats, Darwin wanted to retaliate against Nicole for this, by destroying the car, and tricking her into believing the three all died in it. He initially claimed to be a "paci-fish" in "The Ghost" which he contradicts in later episodes (even later on in the same one).
Darwin has poor memory, likely based on the misconception that fish have a memory of only three seconds. To him, basic spelling is complex, and the only numbers he knows are 2, 7, and 9. Also, in "The Mystery," he fails to remember anything he did the day before, while all of his other classmates remembers clearly.
Despite being human-like, Darwin still sleeps in his fishbowl; however, because he has grown in size, he gets rather squished in there. He also still seems fond of fish flakes, as shown in "The Responsible," and "The Picnic." Other foods he enjoys are cookies, chips, and ice cream.
Throughout the series, Darwin has referred to Richard and Nicole as "Mr. Dad," and "Mrs. Mom," although at some points, he calls them "Mom" and "Dad." Whether this is because he shows more respect for them than a child would, or just the fact that he has some doubts of them being his "parents" is anyone's guess.
Darwin falls in love at first sight with anything that wears a pretty dress. An example of that would be in "The Dress," where he saw Gumball in a dress, and completely fell in love, thinking he was a girl. At that time, he was so in love that he said to the "girl": "I love you", and a photo of him trying to kiss "her" was shown. When the dress later fell onto a fire hydrant, Darwin then fell in love with it. Humorously, Darwin appears to be somewhat of a ladies' man. He has already had three romantic encounters: one with Masami, another with Rachel, and a third with Carrie. Masami chose him as her fake boyfriend, and even went so far as to kiss him. Rachel gave him a kiss on the cheek after he cheered her up at her party. Carrie received a spontaneous kiss from him, with him saying that he has wanted to do that for a long time. He's also shown to be somewhat smooth as to talking to women as shown in "The Bet," when Bobert repeated what Darwin told him to say, Tina was seduced.
In Season 2, Darwin is shown to be angered very easily, and resorts to acts of violence, which have in a few instances bordered on sociopathy.
Also, in Season 2, Darwin becomes more conscientious, as he would sometimes call Gumball out for his wrongdoings, such as his taking advantage of Bobert in "The Bet," and his being insensitive to Banana Joe in "The Promise." As stated in "The Sidekick," Gumball considers Darwin his "guardian," meaning he is the one who keeps him from making bad decisions.
- Main article: Darwin Watterson/Relationships
- Kwesi Boakye (US/UK/AUS/CAN, Seasons 1-2, and most of "The Kids")
- Terrell Ransom, Jr. (US/UK/AUS/CAN, the ending of "The Kids," and the rest of Season 3-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)
- Main article: Darwin Watterson/Quotes
- 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 seems to have feelings for Carrie, as he kisses her in "Halloween."
- 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 can breathe in water, but he is shown to hold his breath, and resurface for air in "The Pressure." He possibly does this because fish cannot breathe chlorinated water.
- 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.
- Apart from Gumball, Darwin is the only character in the series who has made an appearance in every episode to date.
- As stated in "The Spoon," the only numbers he knows are 2, 7, and 9. This may have changed though.
- According to the episode "The Secret," Darwin cannot use the bathroom unless Gumball whistles for him.
- 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 WW1 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.
- According to "The Goons," Darwin is Richard's favorite fish.
- 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 much faster than 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, or even biologically related.
- In "The Hero," it was revealed that he was given to Gumball as a Christmas present. It is also revealed that he had his legs from a very young age.
- 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.
- It is suggested in "The Genius" that Darwin is not legally the Wattersons' adopted son, when Principal Brown stated that he was registered as a pet fish.
- 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 he is allergic to feathers.
- In "The Pressure," Darwin doesn't want to date but in the later episode "The Party," Darwin doesn't know what the word "date" means, suggesting that the timeline is mixed up (technically, "The Party" seems to have come before "The Pressure").
- In "The Burden," it is revealed that Darwin is possessive and fears being lonely.
- Darwin likes Mexican food, as indicated in "The Countdown" (when he asks Gumball not to dis it because it "rocks").