Lord Un

Origins
Not much is known about Un, the deity of the Gray Omen cult, but what is known about him is that two thousand years ago, around the time of Jesus, his followers were at war with the King of the Tier family, who sought to free Earth from Un and his false prophet, Simon. Simon was probably the originator of the Gray Omen cult. His faithful apprentice Father Haller took up his role as cult leader and worshipper of Un.

Biography
Un is unseen throughout most of the pasta, and even when he is seen, only his arm makes an appearance, shown as a gigantic, dark-skinned monstrosity which is too much for a sane person to take. Un has been readied for freedom for years, and recently the stars aligned. Joe Montana, the footballer, became plagued with dreams or nightmares about a cult called the Gray Omen, which haunted him for years, and one day his father was found murdered. Nobody knew what to make of it, and Joe lived by a creepy church which everyone said was haunted, people said Satanists used to frequent the church and screams happened inside at night.

Joe visits the church, and finds it much bigger than he expected, seeing a sort of gigantic university-factory like complex, and hearing cultists as he hides in shelters. Pursued by the cultists, who are discussing the Galactic alignment, releasing Un and searching for a missing girl, Joe eventually finds himself in a library, where he meets Cindy, a beautiful mysterious girl who says she's been held prisoner. She says she was brainwashed by the cult into becoming their slave and now she finds she has a supernatural gift of telekinesis and wants to get revenge. Joe says he'll get her out and they go upstairs, but are accosted by Philip Walker, one of the leading cultists. Cindy and Joe distract Philip Walker and his henchmen, and knock them downstairs, and escape, but Father Haller himself captures them.

Release
After announcing to the cult why he has chosen Cindy for his ritual (because her father defied Un and his false priest Simon) Father Haller announces a new age will begin and prepares to kill Cindy, but she uses her superhuman power to fight back and many cultists flee. They end up dead later, from suicide. Cindy and Joe fight the dark priest Haller, who has only one goal, to kill Cindy, but a portal opens up, and a horrifying dark arm snakes out, clutching for victims. Cindy and Joe knock Haller into the path of the gateway, and a furious, impatient Un clutches his only follower, crushing his ribs, and ending his life, dragging him back into the Netherworld to be eaten.

Un is sealed away as he didn't get Cindy's sacrifice, and the world is safe again.

Trivia

 * This was one of BanningK1979's first Creepypastas.
 * Un may derive from "Unseen" because only his arm is actually seen in the story.