Ultimate Nullifier is the name of several fictional characters appearing in American comic books published by Marvel Comics. They have no connection with the Ultimate Nullifier device.

Mayne is a teenager who appears as a member of the Teen Brigade who possesses technopathy and wields Ultimate Nullifier-resembling ray guns that have the ability to negate superpowers.

This Ultimate Nullifier is a construct that was created from Loki's guilt alongside the other Young Avengers constructs.

An Earth-6160 character inspired by the Ultimate Nullfier appears as a member of the Guardians of the Galaxy.

Ultimaton, also known as Weapon XV, is a living weapon created by the anti-mutant supersoldier program Weapon Plus under orders of John Sublime. The character was created by Grant Morrison and Chris Bachalo, first appeared in New X-Men #143 (August 2003).

Via flashbacks, it is revealed that both Ultimaton and former experiment Fantomex are identical siblings. Created as part of Weapon Plus's Super-Sentinels by employing artificial evolution and nanosentinel technology,they are labeled as exact copies of each other, an anomaly that got fixed by picking Ultimaton for further development inside of The World, Fantomex was discarded to the real world.

Ultimaton escapes from the Weapon Plus facilities, fights the X-Men and is destroyed. He is later resurrected on The World facility and tasked by Fantomex to guard a child clone of Apocalypse. After Evan joined the Jean Grey School for Higher Learning, Ultimaton's function becomes support for Wolverine's black ops X-Force. Furthermore, after Daken's Brotherhood of Evil Mutants kills Fantomex, Ultimaton reverted back to its anti-mutant primary functions and detonates inside of Wolverine's X-Force's Cavern X.

Ultimaton was later revived in The World and under Fantomex's control once more, but still obedient to his role as caretaker of the facility, protecting its assets from intruders.