Ice King

Ice King is a major character conceived to be, but no longer acting as the main antagonist of Adventure Time. Originally depicted as a two-dimensional, humorously over-the-top villain trying to kidnap Princess Bubblegum on a regular basis, the character's personality was subsequently expanded, revealing him to be a kind-hearted but misunderstood old man with completely twisted senses of morality and social behavior, suffering from loneliness and memory loss. Later seasons unveil his tragic backstory, revealing he was once a good human named Simon Petrikov who lost his mind, memories and loved ones due to the magic crown giving him his ice powers.