Nightmare is a demon from the dimension Everinnye, like his "cousin", the Dweller-in-Darkness. Nightmare is dependent on the human race's need to dream. Without this ability, Nightmare would cease to exist, but humanity would go insane. At one point Strange and Nightmare had to join forces to prevent that from happening. Nightmare has run afoul of Spider-Man, Captain America, Ghost Rider, Dazzler, Wolverine, the Hulk, and Squirrel Girl on different occasions. Nightmare also served under Shuma-Gorath and warned Strange that the demon would be a force that even the Sorcerer Supreme would have trouble defeating, and he once joined the Fear Lords, a group of supernatural creatures who fed on fear, to attack Dr. Strange together. Their plans were undone when D'Spayre tricks him into competing with the Dweller-in-Darkness over who could frighten humanity more.