Welcome to Samurai Jack's Place
Samurai Jack is the son of the Japanese Emperor who ruled the area where Aku originally appeared on Earth, and is banished to the future by Aku during their first battle, where he is left in every episode to search for a way home. He was born on the day that his father defeated Aku and he seems to be the only mortal (aside from his father) to be a match to Aku.
Aku is Samurai Jack's arch nemesis. His name means "evil" in Japanese. He is similar to Akuma, the evil demon with burning eyes from Japanese mythology. He is an extremely powerful demon wizard whose primary ability is shape-shifting like the god of evil Amatsu-Mikaboshi, though he possesses many other powers. He requires no food, water, or air and is capable of interstellar travel. He also has the ability to spy on Jack and others from a large sphere he can summon at will in his tower. A significant aspect of the series is that Aku is immortal, and Jack's samurai sword is the only weapon capable of harming and finally defeating him; even the slightest physical contact with the sword's blade causes Aku severe pain, and wounds inflicted by it burn his body and cut away his power. Because of this threat, Aku does not like to fight Jack himself, and only doing so when Jack is incapacitated or without the sword. Aku much prefers to let his minions and bounty hunters do it for him. Aku is also vulnerable to varying degrees to other forms of magical or divine attacks such as the powers and artifacts of gods.