The Black Mass, Also known as 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 gods 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 spawn the demonic sorcerer Aku.
In The Birth of Evil Part 1, the Black Mass was formed from some sort of explosion that occurred somewhere in the outer space. When it began set of to find its prey, most likely the universe itself, Odin, Ra, and Vishnu 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 animals, people, and other forms of life on Earth were devoured by the mass as it continually 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 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 Aku given how it could only be subdued after the three primary gods of three different mythologies fought against it together. Even more worrisome is the fact that, despite its defeat, it demonstrated a capability to inflict harm upon the gods that it fought, specifically in how it nearly killed or corrupted Rama and Ra.
- In some ways, Aku's first tale of fabricated heroism in "Aku's Fairy Tales" greatly parodied the battle between the gods and the Black Mass, in which he assumed a role similar to the gods and added a world-eating dragon in place of the mass.