Mor'du is the main antagonist of Disney/Pixar's 2012 animated feature film Brave, and the titular protagonist of the short The Legend of Mor'du. He was an evil demon bear who was once a human prince and King Fergus' arch-enemy.
Obviously, don't nominate any human characters. Hybrids like Cheetah or The Lizard are okay, as are shapeshifters with one set animal form (eg Professor McGonagall.)
