Samurai Jack & Aku

Samurai Jack and Aku are the central rivals of the animated series Samurai Jack.

Samurai Jack — a disciplined warrior sent into the future after Aku destroys his homeland. He travels through a dystopian world, fighting to return to his own time and undo Aku’s rule.
Aku — an ancient, shape-shifting evil entity who conquers Earth’s future. He is powerful, theatrical, and often humorous, but remains Jack’s greatest enemy.