Born untold thousands or even millions of years ago in the dimension of the vastly powerful energy-entities called the Faltine, Dormammu and his sibling Umar gathered matter to themselves to increase their power, a practice anathema to their fellow Faltine, becoming their dimension's mightiest sorcerers. Ultimately slaying their parent Sinifer, they were driven from their home dimension, the Faltine deeming their garnering of such energy intolerable, and assumed human form to explore others. Their search for conquests brought them to the Dark Dimension, a mystic realm riddled with natural warps into pocket universes within the dimension itself. At the time of their arrival, the Dark Dimensionís multi-species society had been at peace for almost 28,000 years and was in the third millennium of the rule of King Olnar. Despite the warnings of his sorcerer advisors the Mhuruuks, Olnar offered Dormammu and Umar sanctuary and power in exchange for the knowledge of how to shatter dimensional barriers and absorb other dimensions into his domain. After decades of such conquest, Dormammu, whether by chance or design, led Olnar to the dimension of the Mindless Ones, indestructible rampaging dreadnoughts who slew Olnar and many other Dark Dimension denizens. Dormammu and Umar repelled and confined the creatures, using the confusion to murder most of the Mhuruuks, and were hailed as heroes by the Dark Dimension, of which they were proclaimed regents; Olnarís infant son Orini, deemed no threat, was allowed to live under their care. As ruler, Dormammu partially reverted to flaming Faltine form and merged his essence with that of the Dark Dimensionís innate mystic energies, increasing his power enormously.
Little is known of Dormammuís early rule, and since denizens of the Dark Dimension have millennia-long lifespans within a universe whose time passage may not match Earthís anyway, it is almost impossible to guess how long those activities lasted. He warred with several extradimensional rulers and allied with others, forming a pact with Odin of Asgard and even joining the embodiment of Eternity to banish the occult juggernaut called Zom within a netherworldly amphora. Though not common would the clashes or direct alliances of Odin and Dormammu be in the modern-time Marvel Universe, Loki claimed that Odin spoke of Dormammu in comparison to himself, contrary to Dormammuís belief Odin would regard him with "dread." Dormammuís power combined with the force of the Evil Eye was enough to nearly crush the entire Marvel Universe by merging it with the Dark Dimension, showing his potential to threaten entire realities with sufficient might. He apparently observed the Earth dimension for several millennia, supposedly even manipulating the creation of the demon Satannish in Earthís ancient pre-history; he often clashed with Agamotto, the extradimensional entity who appointed himself that universeís first Sorcerer Supreme and held his own against the former, and his disciple, an unnamed tentacled alien. Dormammu at some point knew of both the Celestials and Zeus, and claims he will "burn" the former while his power equals that of the latter. Dormammu also has acknowledgement and respect for the ancient Atlantean mages, even abandoning the Hood for Jennifer Kale, whom he knew has been trained by Dakimh the Enchanter himself, thousands of years later, while Kale's Tome of Zhered-Na warns all sorcerers to reject Dormammu's temptations, indicating even Zhered-Na and the mages of Atlantis knew of his existence and threat. The immensely powerful amulet called the Eye of Agamotto was wielded against Dormammu, as was the mysterious Staff of One of the Minorus (evokers of the Nisanti demon and thus at least indirectly his own power), but Dormammu rarely if ever met true defeat, and in time he ascended the ranks of those mystic beings whose patronage was beseeched by mortal sorcerers.
When Umar went mad after bearing a daughter to Orini, now in millennia-old adulthood, Dormammu used trickery to banish her to a pocket universe, becoming sole ruler of the Dark Dimension and continuing his conquests. Orini became Dormammuís most devoted disciple and raised his daughter Clea in the Dread Oneís service.
Finally, prompted by events that remain unrevealed (though Dormammu's lust for further dimensional conquest to expand his own was certainly far from sated yet), Dormammu targeted the Earth dimension for conquest in 1666, causing the Great Fire of London and using the life-force of its victims to link the two dimensions via Stonehenge. However, Dormammu suffered his first defeat when forced back to the Dark Dimension by the Mystic, Earthís Sorcerer Supreme. In 1692, Dormammu also clashed with Salem exorcist Hiram Shaw, who vied for the Sorcerer Supreme title, and other earthly foes came and went over the centuries, but the Mystic, later called the Ancient One, became his true obsession; indeed, the Ancient Oneís influence spread throughout the multiverse, protecting other realms from Dormammuís grasp. It was through the actions of the Ancient One, aided by the Eye of Agamotto, that he was deemed viable for the role of the Marvel Universe's Sorcerer Supreme. Unable to penetrate the mystic barriers erected by his foe to protect the Earth dimension, Dormammu occasionally acted through earthly pawns over the centuries, as when, in 1888, he was involved in creating Jack the Ripper, perhaps in cooperation with mastermind Fu Manchu, via a mystic parasite later called the Zaniac.
In 1943, Dormammu accepted Baron Mordo, disciple of the Ancient One, into his service via the sacrifice of Mordoís own mother and grandfather; a year later, the Eye of Agamotto was stolen, whether through Mordoís betrayal or not, by Nazi operatives and given to the Red Skull, who inadvertently traveled to the Dark Dimension via its power. When Captain America and Bucky (James Barnes) wrestled the amulet from the Skull, the villain bargained with Dormammu for power in exchange for its retrieval, but the Ancient One sent Sgt. Fury and the Howling Commandos to aid Captain America and Bucky, and Dormammu contemptuously dismissed the Skull from his sight; ironically, Jack the Ripper was one of several time-displaced criminals led against Captain America and Bucky by the sorcerer Terdu later that year. Eventually, Mordo, with Dormammuís patronage, slowly weakened the Ancient Oneís power, a plan eventually halted in 1963 by Doctor Stephen Strange, who became the Ancient Oneís true disciple and ultimate successor; however, Mordo continued to provide Dormammu with human sacrifices.
In recent years, Mordo, evidently displeased with his progress as Dormammuís servant, sought sacrifices for a mysterious entity, the Great Enigma. His efforts won the attention of Doctor Strange and the heroic Spider-Man, and Mordo fled through a portal, only to arrive before the Enigma, none other than Dormammu himself, who had perhaps used the alias to test his hapless catspaw. But Strangeís opposition intrigued Dormammu, who wondered if the Ancient Oneís power was at last faltering if only his successor stood against Mordo.
Shortly afterward, Dormammu sent a ghostly messenger to the Ancient One to announce a renewed intention to conquer the Earth dimension. When Strange traveled to the Dark Dimension in response, Dormammu, surprised that even this challenge did not rouse the Ancient One to action, sent supernatural servitors to bedevil the newcomer. When Strange bested all comers, Dormammu met him in mystic combat, but Strange proved more powerful than anticipated. As he drew upon the Dark Dimensionís energies, Dormammu inadvertently weakened the barrier containing the Mindless Ones and withdrew to force them back. Not wishing Dormammuís subjects to suffer, Strange lent his mystic might to Dormammu, successfully re-sealing the juggernauts. Indebted to Strange for his help, Dormammu felt compelled to end the fight, and Strange made him vow never to threaten the Earth dimension again. Enraged by this turn, Dormammu swore vengeance against Strange, a grudge which even outweighed his hatred of the Ancient One.
Dormammu soon found a loophole to his vow by granting Mordo more power than ever before, for Strangeís murder by a third party would negate the pact. Mordo and his minions hounded Strange across the world for weeks until finally abducting the Ancient One as a bargaining chip to lure Strange to the Dark Dimension. But Mordoís boasting wearied Dormammu, who brought all three Earth sorcerers with him to a neutral realm where, in his own fit of bravado, he summoned the Lords of the Netherworlds, his peers in dimensional domination, to watch him overcome Strange in hand-to-hand combat. However, when Strange seemed to gain the upper hand, Mordo struck him a mystic blow from behind, outraging Dormammuís sense of honor. Banishing Mordo for his troubles, Dormammu faced Strange in a rematch, but fell to his foeís greater familiarity with physical combat. Before the gathered Lords, Strange forced Dormammuís vow to menace Earth no further even by proxy, cementing the Dread Oneís humiliation. However, Dormammu struck a parting blow by extradimensionally banishing Clea, and then manipulating fellow Nether-Lord Tazza into attacking the sorcerer.
Driven to mad fury by their grudge, Dormammu, for reasons unclear, dared to challenge the almighty Eternity himself. Even Dormammuís power was no match for the universal embodiment, who dismissed his foe to the mysterious Realm Unknown, the very dimension where, ironically, Clea now languished. Rallying the demonic Dykkors, banished there by the Ancient One long ago, Dormammu sent wraithlike beings to drain power from the searching Strange, whom he imprisoned. Clea, however, escaped to Earth and mystically influenced Umar, ruling the Dark Dimension in her brotherís absence, to free Strange. The sorcerer confronted his nemesis at the very gateway to Earth he meant to enter, only for Dormammu to be paralyzed by the force of his own vow to leave Earth untouched.
Months later, having reclaimed the Dark Dimension, Dormammu sought a new loophole by possessing the earthborn Strange himself, but met defeat at the hands of Strange and his new allies, the Defenders. Thinking to make Strangeís own friends his catspaws, he then allied with the Asgardian god Loki, Odinís foster son, to manipulate the Defenders into obtaining the talisman called the Evil Eye, whose power he hoped to use to merge the Earth dimension and his own. However, Loki was uninterested in sharing power and manipulated the Avengers into also seeking the Eye, sparking the so-called Avengers/Defenders War. When the two teams discovered the plot, they confronted both menaces and, at the prodding of the mutant Scarlet Witch, the Evil Eye absorbed Dormammu as energy and redirected it at Loki, driving the god from the scene and insane. During this time, it is revealed that Dormammu also appears to possess knowledge of Uatu (having watched the Sol system for billions of years and thus having existed as long or nearly as long as Dormammu has) and his function even before the two first met, and Uatu appeared to know him as well. Though Uatuís presence in the Dark Dimension, as well as his passing Dormammuís magical defenses, shocked and intimidated even Dormammu, despite his possession of the Evil Eye, he was willing to battle even Uatu if the Watcher intervened. A spark of Dormammuís consciousness remained, and with Umarís help, he was reborn on Earth itself. Having thus cheated his vow, and doubtless buoyed by the Ancient Oneís recent death in battle with the monstrous demon Shuma-Gorath, Dormammu was nonetheless betrayed by Umar and banished by Strange, now Sorcerer Supreme, and the earth-spirit Gaea. A subsequent gambit, pitting Strange against the demonic Ghost Rider and the ghostly Bounty Hunter, met no better success.
As a new tack, Dormammu allied with Doctor Doom to channel the power of the mysterious mystic confluence called the Bend Sinister, with Doomís pawn Lucius Dilby attempting to use Strange as a human sacrifice. However, Spider-Man disrupted the ritual, freeing Strange but leaving Dormammu no worse off than before. Perhaps reminded of Mordoís defeat years earlier by Strange and Spider-Man, after ritually maintaining universal balance in a chess match with Odin, Dormammu subtly directed Mordo to time-travel to 1943, where Mordoís grandfather Viscount Krowler, his death still months away, absorbed that eraís the power of that eraís Mordo. Krowlerís Dark Cabal then prepared to grant Dormammu access to Earth by channeling the terror and hatred provoked by Nazi bombings of England. Fortunately, Strange followed Mordo into the past and won the help of Nick Fury and the Howling Commandos; Dormammu was given little time to jog his memory regarding the Commandos when Strange and Fury disrupted the ceremony, scattering Dormammuís mystic essence throughout time and space.
Months later, Strange, following his own arduous confrontation with Shuma-Gorath, healed himself via processes that took him through various dimensions; unknown to Strange, a portion of the incorporeal Dormammu attached himself to his foe during one such passage and, when Strange returned to Earth, possessed the sorcererís body as he had first planned years before. Possession of a human body exempted Dormammu from his vow, and he summoned extraterrestrial sorcerers, including Agamottoís now-renegade tentacled disciple, as his lieutenants. Dormammu vowed to oust the unfathomable Celestials themselves as the greatest power in the Earth dimension, but Strange, his consciousness having fled into a rat, lured Dormammu into blasting him with mystic power, enabling him to rebuild his astral form while his ally Topaz exorcized Dormammuís presence.
Undaunted, Dormammu returned to the Dark Dimension, luring Strange by unleashing the Mindless Ones upon Earth, then trapping him in helpless symbiosis with Clea. Perhaps in nostalgia, he invited Umar to share his reign once more, then banished her anew when she predictably turned against him. Dormammuís invasion of the Earth dimension met unlikely resistance from Baron Mordo, at last weary of Dormammuís abuses and hoping to claim Earth for himself. As Strange and Clea freed themselves, Umar, with Mordo as her champion, forced Dormammu into a compromise, promising him his own dimension to begin anew but neglecting to mention it was that of the Mindless Ones, who were as eager to assault Dormammu in their domain as they had been in his. Umar claimed rulership of the Dark Dimension, with Mordo as consort, but soon Dormammu, in the guise of the Faltine Flyx, lured Clea into gathering mystic allies among the Lords of the Netherworlds to depose her mother. This freed Dormammu to reclaim his realm, becoming more powerful than ever before. Strange, although greatly weakened after losing much of his own power by renouncing the Principalities who patroned him, confronted him alongside a new team of Secret Defenders. Giddy with power, Dormammu gloated that humanityís own evil nature, demonstrated by the horrors of the very wartime era in which he had fought Strange and Fury, proved its need for his rule, then contemptuously dismissed his enemies and, soon afterward, allowed Strange and the human-alien hybrid Darkhawk to seal a breach between the Dark Dimension and Earthís technological Cyberspace, indulgences he doubtless regretted later.
When the Guardians of the Galaxy, heroic adventurers from the 31st century of Earth-691, traveled to the modern era of Strangeís Earth-616, Dormammu, on a whim, followed them back to their home era and attacked their Drydock headquarters, demanding the presence of Doctor Strange, himself known as the Ancient One in the Guardiansí era. The future Strange and his disciple, the alien Krugarr, rose to the challenge, but neither Krugarr, the Guardians, nor their associates the Galactic Guardians could prevent Dormammu combining his own power with that of his future counterpart, from slaying Strange at last. However, careless from his victory, Dormammu allowed himself to be overwhelmed when the Guardians unpredictably teleported him throughout their ship and attacked him in succession with non-mystic powers unfamiliar to him, forcing him to return to his home time and realm.
Whether as a result of his travels through time or of the reality-altering War of the Seven Spheres, Dormammu, despite victory over not one Doctor Strange but two, suffered severe power loss, reducing him to a humanoid husk while Clea led a rebellion against him. Retaining his throne but slow to recover his power, Dormammu bound his essence to a minor demon, Underchild, to enter the Earth dimension unnoticed, where he manipulated the mutant Jonathan White into granting mystic power to others, strengthening his master via millions of worshippers. Although Doctor Strange soon ended this gambit, the revitalized Dormammu launched his most ambitious scheme yet in a war against the demons and death-gods that governed Hell itself, through which he planned to reach Earth. With Satannish as his lieutenant, he captured two-fifths of his targeted regions but was driven out by the united power of his adversaries, rallied by the heroine Hellcat. Dormammuís own realm suffered attack by the vastly powerful Archenemy, whom even the Mindless Ones could not overwhelm, forcing his own alliance with Mephisto and dozens of other demonic rulers of the so-called Splinter Realms before the creature was finally destroyed by the sorceress Magik (Amanda Sefton), but not without severe damage to all realms involved.
Perhaps hoping to recoup his losses, Dormammu attacked the Earth dimension once more. Strange again scattered Dormammuís essence throughout the dimensions, but Dormammu, anticipating this ploy, released the Mindless Ones on Earth; when Mister Fantastic of the Fantastic Four used his technology to force the Mindless Ones back, he inadvertently drew Dormammu back to Earth. Strange nevertheless defeated him, daring to tamper with time itself to ensure victory, but Dormammu resurfaced months later, driven to irrationality and speaking of a childhood and parents he had never had. Umar humored him while, via a shift in the Cosmic Axis, the pairís power increased to such an extent that they were able to overwhelm Eternity entirely. Immersed in Eternityís essence, Dormammu re-made the Earth into his own hellish domain, with a Doctor Strange doppelganger as his lackey; his endeavors were opposed by the true Doctor Strange and the Defenders, but ultimately it was Umar, having taken a liking to the Hulk, who thwarted him, claiming his power for her own and restoring Earth. Dormammu was apparently reduced to a ranting human, but there is little doubt he will return.
Dormammu was eventually reincarnated at the Earth's core as a giant, and imprisoned Gaea. He then battled the Scarlet Witch to avenge his imprisonment in the Evil Eye, but lost. His power was stolen by Umar, and he was expelled from the Earth. He later traveled back in time to 1943. He was driven out of the body of Viscount Krowler by Doctor Strange.
Later, Dormammu took possession of Doctor Strange's body. He was driven from Strange's body by Topaz. He later began a way to regain sovereignty over the Dark Dimension from Clea, and even invaded Earth.
An invasion force of Mindless Ones poured into Times Square and were met by an assortment of superheroes, including Iron Man, Cyclops, Human Torch, the Fantastic Four and Thor. Reed Richards created a device powered by the energies of the heroes present. This served to send the Mindless Ones back where they came, but also recreated Dormammu, whose energies had been scattered. This forced Doctor Strange to try and trick Dormammu into expending his energy before he was back to full power, thus tearing them both apart across the dimensions. However, thanks to the intervention of Spider-Man, the two heroes were transferred outside of time itself, giving Strange the opportunity to send Spider-Man a few moments into the past and prevent Dormammu from ever being released in the first place Dormammu and Umar formed a union between their powers, which was claimed to make them more powerful. They attacked, and overcame a manifestation of Eternity. Dormammu used its power to remake the universe in his image. He was stopped by being engaged by Doctor Strange, the Hulk, and Sub-Mariner, while Umar secretly leeched away his enhanced power, trapping him in a powerless, crippled form. She then left due to lack of interest.
Dormammu revealed himself as the demon behind the Hood's powers, granting him the ability to see through the disguises of Skrulls.
While in Limbo, the recently resurrected Illyana Rasputin attacked various other demons looking for her soulsword and the original bloodstone amulet. This did not go unnoticed by Mephisto, Blackheart, Satannish, Dormammu and Hela.
Dormammu tasked the Hood with finding Doctor Strange and usurping his position as Sorcerer Supreme. Doctor Strange fell to the power of the Dark Dimension, forcing the New Avengers to reach him and battle Dormammu as the fight for the new Sorcerer Supreme continued. Dormammu later assaulted the New Avengers, Doctor Strange and Daimon Hellstrom directly in the Earth dimension, only to find Brother Voodoo bearing the Eye of Agamotto to come forth and intervene against him. Dormammu was exorcised from Parker through the joined efforts of Doctor Strange, Daimon Hellstrom and Brother Voodoo. He was banished to his own Dark Dimension once again, having failed to rise as the Sorcerer Supreme or destroy the chosen one. Loki enigmatically offers to aid the Hood afterwards.
Dormammu was interested in the zombie virus, thinking it as a perfect weapon to make his conquest of Earth far easier, with the Sorcerer Supreme having erected defensive magical screens around the dimensional boundaries to bar him from directly acting on the plane, and commanding the Hood to secure it. Later, when Jennifer Kale became terrified at the sight of the zombie virus mutating into an airborne form, Dormammu appeared before her, and offered her his power. Kale eventually accepts his power when the situation appears hopeless and the Man-Thing falls, with the Hood forsaken.