Kevin makes his first starring appearance in The Hard Goodbye where he kills Goldie while she and Marv are sleeping. Later in the same story, Marv gets his revenge for her death.
Kevin possesses great speed and agility added to his ability to move in total silence. He is an excellent hand to hand fighter, however he makes great use of this long claw like fingernails that are razor sharp.
Kevin is also a cannibal who murders prostitutes then eats them and mounts their heads on the wall as trophies. He believes that he not only eats their bodies, but that he also consumes their souls as well.
Kevin is also known for his smile as it gets mentioned several times in The Hard Goodbye by both Lucille and Marv.
Kevin is never seen speaking but Cardinal Roark (Brother to Senator Roark and Uncle to Junior Roark a.k.a. That Yellow Bastard) says that Kevin spoke only to him and that he had the voice of an angel. Sometime between the beginning of That Yellow Bastard and Hartigans release from prison eight years later, Kevin came to Cardinal Roark riddled with guilt according to the Cardinal about his eating of people and came into his care taking residence on the Roark Family Farm outside Basin City. It was never explained how Kevin got the prostitutes that he killed and ate, only that Cardinal Roark joined him in doing so.
Kevins part in That Yellow Bastard was only a cameo that showed him sitting in the Farm House reading the Bible as Hartigan snuck in to rescue Nancy from Junior Roark. In The Hard Goodbye, Kevin plays a much more substancial role and is killed when Marv lets Kevin's own pet Wolf devour him before finally decapitating him with a hacksaw.
Frank Miller once described Kevin as one of the two "Supernatural Demons" in Sin City. Kevin being the evil one and the character Miho (The Big Fat Kill) the good one.
In the 2005 movie adaptation Kevin is portrayed by Elijah Wood.