They are an offshoot of the evolutionary process that created sentient life on Earth instigated by the alien Celestials, and wage war against their counterparts, the Eternals. According to the account of one Deviant in the 2006 mini-series, the Deviants were created as a delicacy to be consumed en masse by Celestials at periodic intervals once they multiplied sufficiently; however, the veracity of this has yet to be proven.
While the Eternals possess godlike power and are generally physically beautiful (by human standards), the Deviants (who sometimes refer to themselves as 'the changing people') are for the most part hideous (again, by human standards), with each member of their race possessing some random physical and/or cosmetic mutation that is by Celestial design never repeated within the sub-species. Extremely mutated or deformed Deviants are referred to as "mutates" and some of the monsters of myth and legend have in fact been identified as Deviant mutates. Some of these mutations can provide superhuman abilities, but their powers are usually not as great as those of the Eternals.
The Deviants are religious, revering the Dreaming Celestial ("He Who Sleeps in Darkness"). They credit him with their creation and claim that he granted them dominion over the Earth, an agreement they believe was later broken by the treachery of the other Celestials. They have one or more holy books—the only one named thus far being the Book of Krask.
The Deviants had already developed advanced technology such as genetic engineering when humans were still living in caves.
Tutinax the Mountain Mover - A Deviant mutate and a gladiator who aided Dromedan during the time of the second host. He was summoned from past by Zakka, but then killed him. He was eventually returned to own time. In the modern era, he nearly beat Quasar to death when he interfered in a match.
Ulysses Dragonblood - The brother of Odysseus Indigo and former member of the Damocles Foundation. He is able to sedate others with a touch.
Veeg - Also known as Veerg, he is a member of the Damocles Foundation. Veeg secretly aided Sledge, Ulysses Dragonblood, Arcadia Deville, and X-Force in entering the Foundation's Amazon headquarters using the teleportation devices there.
Weller - Member of the Damocles Foundation who received the Celestial Gatherer from Lucas Guthrie. His current whereabouts are unknown.
Yrdisis - An artist and lover of Khoryphos who helped to smuggle the victims of Slicer out of Lemuria until she was uncovered by Brother Visaara. She was later captured by Weird Sisters to aid in resurrection of Maelstrom but was rescued by the Eternals. Her current whereabouts are unknown
Zakka - A toolmaker who built a time-displacer that was able to bring forth ancient warriors. He summoned Tutinax, but was killed by him.
Zona - A member of the Sword of Damacles who could turn invisible and generate electric shocks.
The Deviant Mutates are the creations of the Deviants. Among the known Deviant Mutates are:
Bandrhude - A type of Deviant mutate that were used prior to Great Cataclysm (AKA the Sinking of Atlantis). Bandrhude was later used in the modern era by Ghaur and Kro.
Brutus - A Deviant Mutate who briefly led the Deviants after Ghaur's seeming destruction by the Dreaming Celestial. Brutus organized the Subterranean wars and persecution of Deviant mutates. Brutus was killed when he was exposed as a mutate.
Giganto - A servant of the Mole Man, briefly raised Inorganic Technotroid with its mate, abandoned it after it lost interest. It once made attempt to rule earth, guarded Monster Island for Kro, later became a servant to Mole Man
Glomm - A servant of Dulpus that was defeated by Warbird in single combat.
Gorgilla - Member of the Fin Fang Four. He was formerly used as a pawn by Kro through the Brain Mines and was used to rampage in New York City. Gorgilla later befriended Doctor Druid after being freed by him. Gorgilla was later shrunk to human size by Reed Richard's molecular compactor and became the janitor of the Baxter Building. Gorgilla. helped Elektro, Fin Fang Foom and Googam defeat Tim Boo Ba.
Gort - An agent of Brutus that was defeated by the Hulk.
Karkas - A former gladiator who allied with the Eternals. Karkas was trained by the scholars in Olympia and assisted in Kro’s rebellion against Ghaur. Karkus was later defeated by Reject.
Lizard Men - A race of Deviant mutates in the form of reptilian humanoids that reside in Subterranea. A bunch of Lizard Men were once used as agents of Kro and journeyed to Midnight Mountain and attempted to help capture Makkari
Metabo - A Deviant Mutate that was engineered by Kro. Metabo was able to absorb cosmic energy from Eternals. It was briefly considered for Delta Force.
Minotaur - A monster that was possibly the creature formerly contained within the labyrinths of Aegean sea. The Minotaur battled Ikaris.
Molten Man-Thing - A creature from a volcano who invaded the island of Napuka. It battled Makkari (who was posing as Frank Harper). The Molten Man-Thing was defeated when its heat energy was dissipated by immense fan.
Spore - A Deviant Mutate that was created millennia ago as the ultimate weapon against the Eternals. The Spore gained immortality from consuming Eternals, but was destroyed circa 18000 BC by the Celestial second host. The Spore's particles were incorporated into the cocaine crop of General Caridad. Spore destroyed by Sister Salvation.
Tricephalous - A three-headed monster that lives on Monster Isle and is servant of Mole Man.
World-Devouring Worm - A mutated earthworm released by Dromedan from a "Deviant Coagulation Chamber." It grew larger with each passing second, and could suck objects into its body with a vacuum-like wind. Virako destroyed the World-Devouring Worm by absorbing energies from his craft, destroying himself in the process.
Id - The son of Tantalus and brother of Blackwulf (Pelops and Lucien). Its current whereabouts are unknown.
Khult - A Deviant from Tebbel who is the father of Nirvana. He became servant of Tantalus but usurped his rule of Armechadon at the same time. He helped Blackwulf temporarily slay Tantalus.
Lady Trident - A member of the Peacekeepers who was killed one of Touchstone's bodies. However, she was placed in stasis by another Touchstone.
Mammoth (William "Willie" Amos) - A member of the Underground Legion and possibly the past self of Wraath. His arm was cut off by Blackwulf (Lucian) to save him from the Black Legacy.
Nirvana - The daughter of Khult, wife of Tantalus, and mother of Lucian, Pelops and Id. She committed suicide after giving birth of Lucian. Her body was preserved in undead form by Khult and was later released into death with Lucian's aid
Pandara - A servant of Lord Tantalus. His current whereabouts are unknown.
Schizo - Member of the Peacekeepers and the sister of Touchstone. She was rendered comatose by Touchstone.
Tantalus - The Armechadonian Deviant who is the father of Pelops, Lucian, and Id, and the husband of Nirvana. He used the Peacekeepers as agents on Earth. Tantalus was killed by Blackwulf (Lucian).
Touchstone - Member of the Underground Legion and the sister of Pandara. 24 of her forms were destroyed by Tantalus.
Toxin - Member of the Underground Legion. His armor was destroyed by Tantalus. Toxin later allied himself with Tantalus against the Underground in hopes that he could rebuild his armor. However, he returned to Earth alongside the Peacekeepers.