"Long ago in a distant land, I, Aku, the shape shifting master of darkness, unleashed an unspeakable evil. But a foolish samurai warrior wielding a magic sword stepped forth to oppose me. Before the final blow was struck, I tore open a portal in time, and flung him into the future where my evil is law. Now the fool seeks to return to the past and undo the future that is Aku."
Though he is capable of shifting form into virtually anything he wishes, his standard form is a roughly humanoid being with a black body, a green mouth, and a red beard extending from the bottom of his chin. He also tends to have six horns, four long and two short, extending from his head, and eyebrows made of red, flickering flame. In his standard form, he also tends not to have legs, with his body simply ending at the bottom with robe-like darkness that sometimes manifests as flames, and he also tends to be several stories tall. A deep droning noise is often heard around him when he appears.
Aku constantly antagonizes Jack, often attacking him when he is weak, and other times defending himself from Jack's own gambits. The two seem doomed never to defeat each other, for though Jack has beaten him on numerous occasions, Aku merely transforms into a creature and escapes, usually calling out a taunt over his shoulder, a fact that he is entirely aware of and even lampshades in "Episode XLVIII: Jack versus Aku".
While he's usually presented as a serious and threatening foe, Aku is also a source of comedy in the show, due to his outrageous design and sometimes wise-guy behavior, supported by Mako's over the top voice-acting.
Aku means "Evil" in Japanese. It is written as "悪" in Kanji. The kanji can also be pronounced as "Waru".
Legends of the Multi-Universe (Menslady's story)
He first served Jack of Blades but now serves Galvatron.
The Protectors of the Multi-Universe
Legends of the Multi-Universe (Porfirio's story)
Aku and other villains became the greatest enemy of the Holy Gods. In the end, Aku was finally destroyed by Shenron's divine energy wave, thus putting an end to his reign of darkness for good, especially the Black Mass.