The Black Mass

The Black Mass (Also known as The Ultimate Evil) was a non-sapient life form that roamed outer space, and is presumed to have been an organic manifestation of pure evil, perhaps even the source of evil itself. Before it could fulfill its purpose, which was likely to devour all of creation, three deities: Odin, Ra and Rama arrived to exterminate this great evil. The surviving remnant of the Black Mass that escaped the confrontation eventually landed on Earth and would later become the demonic sorcerer known as Aku.

Biography
In The Birth of Evil Part 1, the Black Mass was formed from some sort of explosion that occurred somewhere in outer space (likely the Big Bang). When it set off to find its prey, most likely the universe itself, Odin, Ra, and Rama arrived to exterminate the mass. After a fierce battle, the three gods finally defeated the Black Mass. Unfortunately, it was not completely destroyed; a fragment of the black mass drifted away from the battle unobserved and crashed into the Earth approximately 65 million years before the rise of Aku. The subsequent impact is believed to have triggered the Cretaceous-Paleogene extinction period, more commonly known as the event which wiped out the dinosaurs.

As life on Earth began to evolve anew, many people were devoured by the mass as it expanded, likely in an attempt to regain its lost power and essence. When the creature approached Feudal Japan, the Emperor (Samurai Jack's father) attempted to destroy the Black Mass with a magical arrow. However, rather than purging the evil from his land, the arrow's poison instead caused the Black Mass to gain intelligence, self-awareness and consciousness, becoming sapient and being set free from the ancient tar pit. Taking the name Aku, the newly-recomposed destructive force then went on to destroy the Emperor's kingdom, until he was sealed away by the Emperor and later destroyed by the Emperor's son using the katana forged by the gods, eradicating the last strain of the Black Mass permanently.

Power and Abilities
The Black Mass was an extremely powerful and volatile force, even more so than its reincarnation, Aku, given how it could only be subdued after the three primary deities of three different mythologies fought against it together. Even more worrisome is the fact that, despite its defeat, it demonstrated a capability to harm the gods that it fought, specifically in how it nearly killed or corrupted Rama and Ra, with Odin being the only one to avoid this attack. It is of planetary size, dwarfing its divine opponents (who are themselves the size of mountains) and capable of shape-shifting during battle, creating temporary limbs as needed. Its tentacles were capable of paralyzing a god that was struck by them; only the intervention of nearby gods could free the victim by severing the attacking limb.

Trivia

 * In some ways, Aku's first tale of fabricated heroism in Aku's Fairy Tales greatly parodied the battle between the three deities and the Black Mass, in which he assumed a role similar to the deities and added a dragon in place of the Black Mass.

Appearances

 * Episode XXXVII: The Birth of Evil, Part 1