Taken from the MSPAWiki~
Karkat Vantas, also known by his Trollian handlecarcinoGeneticist, is one of the trolls and is one of the main characters in Homestuck. His associated zodiac sign is Cancer (♋) and he has horns that are rounded instead of pointed (constantly referred to as “nubby horns” or “candy corn.”) He types in gray with all caps and perfect syntax. His emotes display these nubby horns as the capital letter B, for example, a frowning face is depicted as ):B.
Karkat comes from “Karkata,” the Sanskrit astrological equivalent of Cancer, minus one letter. Additionally, his name may be drawn from “Karkinos,” a giant crab who fought Hercules of myth, also the origin of the Cancer astrological sign. Vantas, on the other hand, is a prostate cancer treatment drug.
His Trollian handle is a play on the medical term “carcinogenesis” which is the development of cancer in the body (or carcinogens, cancer-causing substances), and “carcinology,” the study of crustaceans. The first part of his handle might also be related to “Karkinos”, like his first name.
His online handle could imply either a geneticist studying cancer, or someone who creates cancer genetically. This is proven to be the case later on, as he had genetically bred cancer into Bilious Slick by underestimating the importance of the completion of its genetic sequence, thus ultimately dooming the kids’ universe. Later Karkat tries to think of a title more befitting of him considering the apparently doomed life he created via Ectobiology. Ironically, he can’t think of the obvious choice present in his trollian handle.
His weapon of choice is a sickle. This is most likely to contrast or even complement John’s hammerkind, as the hammer and sickle are the symbols of communism and the Soviet Union (this was later directly referenced by Dave), or it may resemble a crab’s claw. It may also be a reference to sickle cell disease, or anemia, a sickness of the blood caused by a genetic mutation, which is suitable since Karkat himself has a genetic mutation that makes his blood unique.
Karkat is a very crabby troll, which is a pun on his sign. In fact, most people under the Cancer sign are said to be moody and crabby like he is.
Karkat was the leader of the Red Team, and leader of the joined teams.
Personality and Traits~
Karkat is a crab in more ways than one. He constantly insults others in the style of a stereotypical internet troll, supporting his arguments with what seems to be empty logic. Jade has even gone to the point of flipping out at Karkat. In keeping with the crab appleasshole theme of his personality, he rarely smiles. He is also often seen screaming, pounding his fists against his keyboard, or generally raging when talking to anyone. He is not particularly patient when explaining himself, making even his most sound advice appear to be random insults.
One of the only times Karkat smiles
Somewhat similar to Jack Noir, Karkat is ruthlessly ambitious and will grasp at any opportunity for power, but he just doesn’t have the subtlety of his troll compatriots and ends with the sharp end of the stick more than once. His real strength is to shepherd his boneheaded troll friends into following a plan, which just gives him another excuse to go off the handle when something does not go according to it. Despite his arrogant and volatile behavior, he proves to be a somewhat effective leader of the twelve trolls. This is acknowledged by some of the trolls and is even stated so by Vriska.
Despite his flippant demeanor, he also seems to care quite deeply for his friends’ well being, judging from his tearful reaction to Sollux’s apparent death, his seemingly genuine desire to help Eridan and Tavroswith their relationship issues with Feferi and Vriska, respectively, and his willingness to revive Kanaya. Towards the end, Karkat seems to show a softer side that hasn’t really been shown before. In his final memo, future Karkat leaves a rather emotional story shortly before Kanaya responds to it. At this point he treats her in a friendly and polite manner, something that he’s done only with a select few before. He also shows concern that his friendship with Dave will not persist after they meet with the other humans, and later he shows great concern for Terezi when it is discovered she is no longer blind.
Unlike other trolls, Karkat doesn’t “wear his blood color on his sleeve,” in either the figurative OR literal sense, and is very defensive when asked about it. When he is stabbed by Jack Noir, it turns out his blood is bright red, a nearly unique mutation among trolls, one that he is extremely ashamed of. He and Jack Noir form an alliance when it is revealed that they have the same color of blood, a revelation that shocks Karkat. It is believed that this insecurity is what spurs Karkat to be so crabby all the time.
Karkat uses rich and imaginative language in his particular fashion (e.g. YOU ARE SUCH AN IGNORAMUS I COULD SHIT MILES OF RAGE SNAKE TO CHOKE YOU TO DEATH), but not to the extent of a typing quirk.
Karkat is not nearly as bloodthirsty as some of the other trolls (like Vriska or even Kanaya), and has trouble jumping to action when shit hits the whirling device. If things go off plan and he’s not nearby, he gets pissed off and starts yelling at the related parties. If he -is- nearby he either tries to devise a working plan or stands there in shock.
Despite being possibly the grouchiest troll on the whole planet, Karkat relates well to people, possibly because he is mentally stable, by troll standards, and believes that showing many kinds of pity is the best way to have the capacity to hate. He usually stops insulting and whining whenever the other troll mentions he or she has some kind of significant problem that isn’t worth making fun of. He is the go-to guy for several of the trolls with romance issues, like Tavros and Eridan, and even unwittingly advises Vriska, as well as Kanaya. Ironically, Karkat admits that he has problems with relationships, particularly blackrom, and thinks he sets his standards too high. His inclinations towards redrom are strictly private. It is also implied that Karkat has unrequited flushed feelings for Jade.