Long ago in the vastness of space, a great formless evil appeared. Before the darkness could do harm to the universe, it was set upon by the kings of three religions: Odin, the one-eyed king of Asgard and the Norse Gods; Ra, the sun god and king of the Gods of Egypt; and Vishnu, the supreme being in Hindu mythology. So fierce was their attack on the shadow, that it was completely destroyed, save for a small fragment that was flung aside in the heat of battle. For ages the fragment drifted through the cosmos and eventually fell to Earth, and caused the impact event that wiped out the dinosaurs when it landed. The land around its impact site eventually formed into the islands of Japan, where it slowly grew and spread like poison over the course of eons, creating an ever-spreading forest of black spikes that devoured any who entered. Eventually the forest grew so large that the Daimyo of the land (Jack's father), decided to kill the evil at its source. Armed with a magic oil given to him by Buddhist monks, the Lord and his cavalry rode into the heart of the forest, the Lord himself the only one to survive. Once at the black lake at the forest's center, the Samurai Lord doused an arrow into the oil he was given, lit it with a green flame, and shot it into the lake. Instead of destroying the evil however, the magic arrow gave it both a will and consciousness, thus the demon Aku was born. Aku proved to be unstoppable, so with the help of the three gods, Jack's father forged a sword capable of harming him. With it, he was able to defeat Aku and somehow turn the demon into a black tree. This imprisonment lasted less than a decade however, as a solar eclipse released Aku upon the world once more. His name means "evil" in Japanese. He is similar to Akuma, the evil demon with burning eyes from Japanese mythology (which may also be another source for his name). He is an extremely powerful demonic wizard whose primary ability is shapeshifting. 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. While he is usually presented as a serious and threatening foe (as well as being pure evil), Aku is also a source of comedy due to his outrageous design and sometimes wise-guy behavior.