Set is the Egyptian god of the dead and chaos and the brother of Osiris.
Set killed his brother, Osiris with the Sword of Osiris.
The sorcerer named Magus was inspired by Set's teachings, which made him influence Mathayus to find the Sword at the Underworld and sacrifice a victim who would be a vessel for Set. As Magus got killed by Mathayus, he became a vessel for Set, who was quickly exiled by Mathayus.
Behind the Scenes
Voice actor Daran Norris provided the voice of Set.