M.O.D.O.K. is a character of the Marvel Comics universe. He was once George Tarleton, a man of unspectacular intelligence who was used by terrorist organization A.I.M. (Advanced Idea Mechanics) in experiments to enhance mental powers. The procedure initially transformed him into M.O.D.O.C., the Mental Organism Designed Only for Computing. However, with his new super-intelligence, he quickly seized leadership of A.I.M. by force, renaming himself M.O.D.O.K. -- the Mental Organism Designed Only for Killing.
Alongside his incredible intelligence, M.O.D.O.K. possesses powerful psychic abilities. However, the experimental procedure greatly expanded his cranium, leaving him physically as a gigantic head with a body and limbs incapable of supporting its weight naturally. He rests in a special hoverchair that provides him mobility, as well as defense in the form of concealed weaponry.
M.O.D.O.K.'s inherently ridiculous nature makes him perfect for comedic takes on the character, as seen in Marvel's What The--?! shorts, the Marvel Adventures comic book line (in which, to tone him down for younger audiences, he becomes the Mental Organism Designed Only for Conquest), and the Super Hero Squad cartoon and video game series. Meanwhile, his intelligence and aforementioned love of killing make him highly usable in serious stories, such as his alliance with the evil genius team The Intelligencia in a Hulk storyline.