The "Black Sun" who lives in the underworld in Babylonian lore.
His original name is Aciel, which the Jews borrowed from a Babylonian god, and called him the "King of Gehenna." But in some Asian faiths, all things are reborn only by darkness, so Alciel is not all bad.
Trivia
Despite several compendium entries stating that Alciel is derived from Mesopotamian culture, there is no evidence to support this claim; it is likely a conflation resulting from the use of the word "Chaldean" to describe Alciel in the occult book The Woman's Encyclopedia of Myths and Secrets, by Barbara G. Walker. At the time the book was written, "Chaldean" was often used to describe figures in occultism, not figures related to the historical Chaldea of Mesopotamia.