Aku was Evil Incarnate; he embodied the very essence of an evil overlord. Cruel and domineering to all that he met, it was obey or be obliterated with Aku. Arrogant, temperamental, callous, and sadistic by default, Aku ruled the Earth for thousands of years and did not take kindly to disobedience. Aku was responsible for countless genocides, with cities, towns, villages, and small settlements being completely destroyed, alongside all their inhabitants, while nature itself was left to rote.
*"Long ago in a distant land, I, Aku, the Shapeshifting 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."*
*He was inside his den in big volcano*