AT Villain set - Ice Monarch

He's the designated villain...  or antagonist.  When the show wants him to be.  He did start out as a villain, though.  A sympathetic villain to be sure, but still.  The Ice King just so happens to be my favorite character in Adventure Time, though if I were to describe why, I'd be here all day.  I will say this, though, there seems to be a definite change in the Ice King's personality from the beginning of the series to where he is now.  In the beginning, he was more prone to theatrics and hamminess with what he says, now he's a lot more casual with everyone, except when he really gets intense while fighting.