|The following information is from the Adventure Time comic book series. It may not be part of the same canon or continuity as the animated series.|
Arklothac is a multi-dimensional candy god-like being that appears in the comics. He is a giant red monster that sports an Italian chef mask on his head. He was summoned from beyond time and space by the witch Janice Bizzlethatcher, and was later defeated by Finn with the Moon Sword.
He then returns with his fellow Cosmic Elementals to rain chaos on the world and presumably kill the main cast excluding Finn. Later, Penelope, with the Moon Sword and the help of Finn, killed him and then had him erased from existence with the other.