Dormammu

As the Sorcerer Supreme of Earth's dimension, Doctor Strange often calls upon sorcerous entities of other realms to endow his spells with power. Phrases like "the hoary host of Hoggoth", or "the crimson bands of Cytorrak" often entered into his spells, as did calls for aid from the dread Dormammu. Little did readers know that behind this name lay a malevolent evil.

Dormammu and his sister Umar were natives of the dimension of Faltine, though for unrevealed reasons, they were exiled from that dimension. They ended up in a small pocket dimension known as the Dark Dimension which was ruled by a sorcerer named Olnar. The siblings promised the sorcerer-king that they could increase his power by breaking down the dimensional walls between the Dark Dimensions and other surrounding dimensions. Ignoring the warnings of other wizards in the kingdom, Olnar agreed and, placing Dormammu and Umar as his trusted advisors, began absorbing other dimensions into his own.

This path soon became Olnar's undoing as one of the dimensions that was absorbed contained beings known as the Mindless Ones. These creatures are humanoid in appearance, though they have an orifice where their faces would usually be that they can project energy from. These creatures live only for destruction and soon were laying waste to the Dark Dimension. Olnar was killed in their initial assault from which Umar and Dormammu barely escaped. Knowing that they would be blamed by the other sorcerers of the land for the destruction, the two struck first, causing the wizards to be struck dumb and therefore powerless. They then trapped the Mindless Ones behind a mystical barrier. All of this cost Umar greatly and she was forced to spend a long period recovering. Dormammu was named the new leader of the realm, while Olnar's son Orini grew to adulthood.

Dormammu chose to transform himself into pure energy to better tap into the mystical energy that was at his disposal. For this reason, Dormammu appears as a humanoid form with a flaming head. The flames are the flames of Faltine and surround the head of the leader of the Dark Dimension.

After ruling the Dark Dimension, Dormmamu set his sights on the dimension of Earth and so ran afoul with Doctor Strange, the Sorcerer Supreme. The two first battled in the Dark Dimension, where the two wizards eventually were forced to combine their might to return the Mindless Ones to their mystical confine. Dormammu agreed not to attack Earth and to leave his niece, the sorceress Clea alone after she aided Strange against him. Dormammu did not honor his agreement however.

Later Dormammu decided that he could defeat Doctor Strange by traveling into the past and becoming a human being and killing Strange before he became a threat. Strange and Clea traveled into the past and opposed the dread Dormmamu, eventually dispersing his energy form over many dimensions. Seemingly completely defeated, the rule of the Dark Dimension passed to Umar.

Umar was later deposed by Clea, but in the recent past, Dormammu has returned and retaken the throne of the Dark Dimension.