Not much is known of the "Nightmare Master's" past, but Terinios grew up abused by his stepfather. Terinios hated his stepfather for his ill-treatment, so much so that he later learned the dark arts to create and manipulate dreams. Upon learning the strongest nightmare incantation, Terinios unleashed upon his sleeping stepfather the most powerful of night terrors. His stepfather died from a heart attack due to that act of revenge.
Terinios used his powers to murder and to create terror for those he encountered.