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 also served under Shuma-Gorath and warned Strange that the demon would be a force that even the Sorcerer Supreme would have trouble defeating.
Nightmare once joined the Fear Lords, a group of supernatural creatures who fed on fear, to attack Dr. Strange together. But their plans were undone when D'spayre tricks him into competing with the Dweller-in-Darkness over who could frighten humanity more.
Nightmare is the father of the Dreamqueen, a similar but lesser being who rules her own "dream dimension".
Nightmare's realm is not part of The Mindscape, but the Sleepwalkers are aware of him and consider him an enemy.
Because Sleepwalkers do not have to sleep, Nightmare has never been able to affect or dominate them. He sought to do this through the hero Sleepwalker, who had been connected into the brain of the human Rick Sheridan. Nightmare sent Sleepwalker back to his own realm, with a monitor to assure the hero Rick was not being tormented. Rick was being tormented, with the intent of driving Sleepwalker mad and thus giving Nightmare access the minds of Sleepwalker's people. The hero was not fooled and sacrificed his return home in order to stop Nightmare.
Later, Nightmare was able to access human minds through the concept of the 'American dream'. Many people who were deeply patriotic or had achieved a degree of success through hard work were going on violent rampages. Nightmare was soon stopped by the combined forces of Captain America, Sharon Carter and S.H.I.E.L.D..
Nightmare appeared in in the "Secret Invasion" arc of The Incredible Hercules. Hercules and the God Squad, making their way to the Skrull gods' realm, require a map of the Dreamtime, and barter with Nightmare for it. Nightmare agrees, in exchange for access to the fears of the five gods; however, he actually intends to use these divine fears to conquer the world. Hercules and the others escape his realm, having stolen the map via trickery.
Nightmare is now plotting to conquer the entirety of fiction, adding it to his realm of nightmares.
We Had Both Forgotten Our Last Trip to a Huge DIY Superstore, a Journey into the Seventh Level of Suburban Hell; Keeping It Together
May 05, 2011; Byline: Kate Kerrigans ONCE a high-flying magazine editor in Dublin, living the classic, harried executive lifestyle, Kate...