The Watcher

 Origin: 

He was born in pure darkness, during a bloodbath of a war, surrounded by strange figures. His mother died during birth, and his father killed by Cultists, who raised him with the purpose of being kept for the future to bring their race back. During his training, he became skilled in almost all areas, mainly magic and swordplay. He was put into a type of sleep that froze him to let him survive the horrors of time. He went on to seek the Daedric Princes to become much more powerful. He eventually met them all, and went on to become so powerful, he made the Daedric Princes themselves fear him as they worried he'd eventually be able to collapse their realms. They used all their power (along with the help of Tim Cabbage) to trap him on a desolate island, until 15E, when Lord Sam VI of the Dwemer accidentally released him. He went on to cause the worst and largest genocide in the history of Nirn, and it was only the combined power of Tim Cabbage, The Daedric Princes, and the Divines to end the Age of the Watcher.

Timeline:

Merethic Era - The Watcher was born, in a place lost to time, and sealed underground for a long time.

1E - The Watcher mastered magic from the Daedric Princes, and received his signature armor.

1E 204 - The Watcher is sealed away by the Daedric Princes to a remote island surrounded by magical rocky walls.

15E - The Watcher is accidentally released by Lord Sam VI of the Dwemer.

15E to 19E - The Age of the Watcher begins.

16E - The Watcher kills Voon Spoon and Randy.

17E - The Watcher sends rogue Dwemer to find the hiding Dwemer.

18E - The Dwemer evacuate to Goblin Town.

19E 1 - A massive dip in the Goblin population occurs, as well as all the other races, due to the explosion of an Elder Scroll.

The Watcher's location after 19E 1 was unknown for a long time after escaping, although both Tim Cabbage and The Watcher are the only to know the true consequence of the destruction of an elder scroll.

In 20E, genocides, murders, etc. started throughout the world. Along with plagues, diseases, etc. The Watcher, is to blame.