Countless eons ago, Dormammu was spawned a powerful Faltine known as Sinifer. Dormammu spent his early life in his home dimension, the Faltine Dimension, growing in power by absorbing physical matter into himself. When his father tried to stop him from absorbing physical matter, Dormammu and his sister Umar worked together to convert Sinifer into matter himself, essentially killing him. This action led to the banishment of both Dormammu and Umar from their home dimension. The two traveled throughout the multiverse, hungry for matter and conquest when they stumbled upon the Dark Dimension. There, Dormammu met their king Olnar, who offered the two power and peace in return for learning how to merge dimensions as a means of conquering. After many years of the trio conquering other dimensions, Dormammu led Olnar to the dimension Mindless Ones, where the king met his demise. Using his position as a hero of the Dark Dimension, Dormammu was able to usurp power from Olnar's infant son, merge the energies of the Dark Dimension into himself to drastically increase his power, and become the realm's immortal ruler. Ever since then, Dormammu has kept up his endless mission for conquest, setting a particular interest in Earth where he would meet constant conflict with the Sorceror Supreme known as Doctor Strange.
Incredible Intellect: As a result of his dimension hopping and ancient age, Dormammu is very intelligent. He has shown to be a brilliant strategist and manipulator in combat, successfully ruling the Dark Dimension for eons.
Faltinian Physiology: Dormammu's origins as a Faltine grants him various abilities.
Energy Composition: As a Faltine, Dormammu is entirely made of magical energy.
Body Forming: By manipulating the magic of his body, Dormammu can alter his body's shape, size, and color on a whim.
Regeneration: If he is ever hurt, Dormammu can just reform his body at will.
Godly Physique: As a godlike being, Dormammu has strength, agility, and durability far beyond that of most mortals.
Magic: Dormammu is naturally talented in the ways of magic as a Faltinian.
Flames of the Faltine: The natural magic of his species, Dormammu can produce magical flames from his body powerful enough to sear godlike entities. This fire magic has harmed Ghost Rider by use of Doctor Strange, who is a lesser user of the spell. Though mostly an offensive spell, Dormammu can also use the flames to create protective shields or interdimensional portals.
Banishment: Dormammu can banish creatures to a pocket dimension of his choosing.
Dimensional Fusion: To conquer another dimension, Dormammu is capable of physically combining it with the Dark Dimension.
Dark Dimension Enhancement: As a result of so deeply fusing with the natural energies of the Dark Dimension, Dormammu is more powerful there.
Reality Warping: Due to his role as leader of the Dark Dimension, he can manipulate its laws of physics and logic at will while there.
Immortality: Dormammu is naturally immune to the effects of time and natural diseases, meaning he can live forever unless killed in battle.
Arrogance: Although Dormammu is an incredibly powerful godlike magic being, he also thoroughly believes he is a god amongst gods. His arrogance has led him to underestimate and toy with even very powerful foes before.
Temper: If his ego is ever harmed from defeat, Dormammu can be blinded by an overwhelming rage. While making him more tenacious, it also clouds his judgment and can lead to poor planning or unwise decisions, such as the time he challenged Eternity to a death match out of sheer anger.