Omega-level mutants

Omega-level mutants are the mutants with most powerful potential of their mutant abilities, appearing in American comic books published by Marvel Comics.

Publication history
In August 1986, the term was first introduced by Chris Claremont in Uncanny X-Men #208 as "Class Omega", but wasn't explained except referring to an exceptional level of power. It was first used to describe Rachel Summers' powers on which Nimrod reported that "Upper limit of target-subject's abilities has yet to be determined."

The term was not seen again until the 2001 limited series issue X-Men Forever #3, where Professor X described Iceman and Marvel Girl's "Omega level mutant abilities" having unlimited potential. For a time, no firm definition was offered in the comics and the term "Omega-level mutant" was simply used whenever a writer wanted audience to know that the character was a big deal. This led several conflicting opinions and debates among fans as to who or what qualified as omega-level.

In July 2019 during X-Men relaunch of Krakoan Age, Jonathan Hickman provided an official definition in House of X #1 and listed fourteen Omega-level mutants alongside their respective omega power.

In November 2020, a new status quo for Powerhouse, who was considered Omega-level mutant was established that he was not a mutant in Fantastic Four, vol. 6 #26. Then X-Men's senior editor Jordan White had disagreed with this decision and the change was made due to character's affiliation with Fantastic Four. However March 2024, Marvel Comics reinstated his previous status as Omega-level mutant by revealing that he was repressing his powers as per Fantastic Four, vol. 7 #18.

After the X of Swords event in 2020, a large number of Omega-level mutants were introduced from the Arakko and its governmental body, the Great Ring of Arakko was composed of Omega-level mutants (excluding the adjunct and night seats).

In January 2022, it was revealed that mutants can enhance (at least to some extent) their power to omega-level by further training as Synch had shown potential to achieve omega-level status in X-Men, vol. 6 #7.

Definition
Definition given by Jonathan Hickman [emphasis in original]:

"Omega Level Mutant: A mutant whose dominant power is deemed to register – or reach – an undefinable upper limit of that power's specific classification.

For Example: Both Magneto and Forge are the most powerful mutants of their power types on the planet Earth [Magnetism and Technopathy, respectively], but what makes Magneto, and not Forge, an Omega level mutant is that the upper limit of Forge's measurable powers could hypothetically be surpassed [and, in fact, has by multiple humans on the planet], while the upper limit of Magneto's power cannot be surpassed in any measurable fashion.

Note: Omega level is a classification of a single mutant power. While it is quite common that mutants manifest multiple powers, only one is normally of Omega level.

For Example: While Jean Grey is both a telepath and a telekinetic, she is only an Omega level telepath."

Multiple mutants can achieve the upper limit of a power at the same time on which Jordan White stated that he didn't believe there's anything in the definition that said there can be only one.

"For Example: Both Kid Omega and Jean have the highest upper limit for telepathy that there could be possible."

Reception
In April and July 2019, Charles Pulliam-Moore from Gizmodo and Thomas Bacon respectively had highlighted the challenges that might come with classifying Omega-level mutants. Charles stated that Omega-level mutants are singled out for being unique but there are also characters with similar powers to them and challenges might come for writers to imaginative things when questions would be asked what can these mutants can do when they are at their upper limit. While Thomas wrote in Screen Rant that a writer writes any superhero as very powerful which could be pointed by fans to add their favourite character into the ranks of Omega-level mutants and writers might come under immense pressure from it.

Regarding Omega-level mutant classification, Amer Sawan of CBR in April 2023, commented that one downside to it was that the system to classify Omega-level mutants changes frequently with constantly shifting nature of the powers and due to this, some mutants who had done incredible things with their powers would lack recognition for being denied the status of omega-level.