En Sabah Nur stated that he was the first mutant was often stated to be, and thought himself to be (his name meant "The First One"), although Selene predated him by 12,000 years at least.
However, in X-Force: Necrosha, new information was revealed that showed Selene, the Black Queen, was the first mutant, having been born in 15,000BC, some twelve-thousand years before Apocalypse. Selene was no stranger to the X-Men at this point, having debuted over 25 years earlier in New Mutants (1st series) #9.
Early X-Men issues introduced the original team composed of Cyclops, Marvel Girl, Beast, Angel, and Iceman, along with their archenemy Magneto and his Brotherhood of Evil Mutants featuring Mastermind, Quicksilver, Scarlet Witch, and Toad.
Long-time fans of the X-Men franchise will not be surprised to learn that the title goes to Charles Xavier's own son, David Haller, aka Legion, who has the power of countless Omega-level mutants trapped in his usually unstable mind.
The Legion (Personality 005): Self described as "real me" and by Magik as a "God-Mutant". He is able to warp reality to his will and manipulate time. Using these powers he created the Age of Apocalypse and eliminated the Elder Gods of Limbo.
An Omega-level mutant is one with the most powerful genetic potential of their mutant abilities. The term was first seen in the 1986 issue Uncanny X-Men #208 as "Class Omega", but was completely unexplained beyond the obvious implication of it referring to an exceptional level of power.
In the comics, Namor was also the first mutant introduced in 1939, although he wasn't called a mutant until after the X-Men's introduction in 1963. It appears that the MCU is finally ready to start introducing mutants officially, and Namor is one of the first to make that leap.
Namor is considered an ageless character, and the exact age of Namor is not specified in the comics. In comparison to Logan (Wolverine), it is stated that Logan was born in the late 19th century, and he is given a mutant ability to heal rapidly and to remain youthful, and he is considered to be over 100 years old.
In the timeline of the Marvel Universe, it is believed that Namor was born around the year 1920 making him over a hundred years old. Read one of his pivotal appearances (alongside original Human Torch Jim Hammond) in MARVEL MYSTERY COMICS (1939) #8.
Although Thanos would undoubtedly have the edge over Apocalypse were he to use the Infinity Gauntlet, without it, Thanos could very well meet his match. Though both are incredibly powerful and intelligent, Thanos is held back by his obsession with death, which would cause him to overlook some of Apocalypse's power.
Typically portrayed as a foe of the X-Men, Mystique has been both a supervillain and an antiheroine, founding her own Brotherhood of Mutants and assassinating several important people involved in mutant affairs; she has been stated to be over 100 years old.
Although able to control any fire within his vicinity, Pyro is unable to generate and project fire himself without an external source. After joining the Marauders, Pyro often teams up with his teammate Lockheed, who has the ability to breathe fire, fueling Pyro's living flame.
Essentially, an Omega is a mutant with a specific power greater than any other of the genus. While there are many ice powers in Marvel's Earth, only Iceman's is registered to be as powerful and iconic. While there are many telepaths, only Jean Grey is the most renowned.
Wanda ceased to be a mutant in Earth-616 in a controversial Marvel Comics retcon, but in this reality, she was considered an Omega-Level Mutant capable of telekinesis, telepathy, and more.
Wolverine is considered a Beta level Mutant. Mostly though, he's just not an Omega class Mutant. In the mainstream Marvel 616 continuity they mostly only use the Omega class to describe the very powerful Mutants.
Isca The Unbeaten is a character created recently in the X-Men comics. Her power is being, quite literally, "cursed to win", which prevents her from ever losing or being on a losing team.
Batman is one of the oldest superheroes still running, weighing in at almost 80 years and counting. Yet Bruce Wayne hasn't really aged at all, seemingly the same age today that he was in his debut back in 1939.
Magik. The most powerful member of the New Mutants is Illyana Rasputina. This is because she is more than just a mutant. She first appeared as Colossus's little sister, and soon she proved to have mutant powers and joined the New Mutants.
