Aku (Samurai Jack)

Aku is a demonic shadowy figure and the main antagonist of Cartoon Network / [adult swim] animated series, Samurai Jack. Born from a cosmic black mass of darkness, Aku was an evil, shapeshifting entity that has taken over the world and ruled it for countless eons after capturing Jack's father which left him and his mother to leave.

Although he was capable of shifting form into anything he wants, his standard form was humanoid with a black body, green mouth, and a red beard extending from the bottom of his chin. He had six horns, four long and two short, extending from his head, and his removable eyebrows made of red, flickering flame.

In his standard form, he often doesn't have legs, with his body simply ending at the bottom with robe-like darkness that sometimes manifested as flames. Since, he was a shapeshifter, he was several stories tall. Whenever he appears, a deep droning sound was heard.

He was also been infamously known for taunting Jack to ever get back to the past and in order to save his people until in Episode CI, where he finally did it and slayed Aku along with Ashi.