Great Evil Beast

The Great Evil Beast, also known as The Great Darkness or The Ultimate Darkness, is a powerful cosmic entity that appeared in the DC Comics Swamp Thing storyline, "American Gothic."

This being is outside of The Presence's creation. This is no fallen Angel or Leviathan, this is the soul of darkness itself. A complete absence of divine light. This being is in every way equal to the power of the Presence, but his opposite who existed before Creation.

When the earth-shattering events of the Crisis on Infinite Earths struck, a group of mystic madmen calling themselves the Brujería attempted to conduct a mystic ritual to contact the Great Darkness; unsurprisingly, it went awry and instead the entity awoke as a furious beast, unknowing of its own power and confused about its existence.

It ended encountering a number of mystical heroes (Etrigan, Doctor Fate, the Spectre), who unwittingly angered the being and directed it against Heaven, leaving only the defeated heroes behind. They did this unknowingly, despite their best intentions; Etrigan taught it darkness was evil, Dr. Fate told him that evil was despisable, and the Spectre instructed it with the concept of Revenge. Infuriated, the being sought to assault Heaven to demand answers from the Presence as to its existence, trampling all it crossed paths with. This power was so huge, it caused Hell's main three figures - Lucifer, Azazel and Beelzebub - to form a triumvirate to defend themselves should the Great Darkness decide it wanted Hell as its realm. A different faction, led by the Demons Three, banded together to follow the Darkness, whom they saw as the ultimate sin and evil.

However, before the Great Darkness reached the gates of the Silver City of Heaven, it encountered Swamp Thing, who taught it the concept of evil and good, life and death, intertwined so that one could not survive without the other. The Great Darkness then extended its hand, and something happened that nobody had foreseen; the Presence extended His. When both Hands touched, both the ultimate light and the supreme dark merged, forming the perfect balance as a form of Yin/Yang.

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Wikipedia