While Knight Terrors has introduced a whole new horror to the DC Universe in the form of the dreaded Insomnia, the self-proclaimed God of Nightmares is far from the only villain with an important role to play in these grotesque proceedings. In fact, despite all his efforts and apparent rise to power, Insomnia isn't even the one at the heart of the slumber that has grasped nearly the entire globe. Instead, it is none other than Doctor Destiny who holds the key to these nightmarish events, even if he isn't the one controlling them as they unfold.
Source：https://www.cbr.com/dc-knight-terrors-doctor-destiny-trivia/
