Immortus is said to be the final incarnation of Kang the Conqueror, his last incarnation where an older and wiser figure would emerge from the failures of his conquering days, preferring to monitor time rather than rule over it. Immortus was born on Earth sometime in the 31st century. This is an alternate future from the Guardians of the Galaxy: in Immortus' reality, the Badoon never conquered Earth. After pillaging the time stream using his technological powers to subjugate different time periods, he settled into the role of Rama-Tut.
As Rama-Tut, he once captured the Fantastic Four and attempted to marry Sue Richards, the Invisible Woman. Curiously, it was later revealed that Immortus is a descendant of his namesake, Nathaniel Richards, the father of Mr. Fantastic, making the Invisible Woman a great aunt (many times removed) to Immortus/Kang/Rama-Tut.
Immortus was created by Stan Lee and Don Heck in 1964 and first appeared in The Avengers # 10.
After further adventures as both a despot and a benevolent ruler, an older and more philosophical Rama-Tut traveled to Limbo to finish his remaining years in relative peace. However, the Time Keepers approached Rama-Tut and offered him immortality in return for serving them as guardian of part of the timestream, covering 80 millennia as a monitor of the fabric of time itself.
At this point, he became Immortus and worked to repair the damage that he and his other incarnations had done to the time stream. He maneuvered through the timestream, focused on preventing time paradoxes, and eliminated unnecessary time travelers, such as when he removed Mjolnir's time-traveling ability with Thor's permission after manipulating him into "saving" the planet of the Space Phantom by using his time travel powers to stabilize the planet. In reality, not only was there no planet that the Space Phantom belonged to, but they were actually citizens of Limbo itself: millennia had converted them into twisted creatures that served Immortus and his will only.
When the Time Keepers became aware of some possible futures where the Avengers had left a legacy that would be a universal dictatorship, they tasked Immortus to prevent this future from ever happening. Immortus started a long-term plan of manipulating the Avengers/others and various events in their history, only to realize later that he accidentally created the very future he was supposed to prevent. Afraid of the Time Keepers destroying the world and the Avengers, Immortus asked for one final attempt. To do this, he planned to kill Rick Jones to prevent him from releasing the Destiny Force. However, this plan was endangered when his younger self, Kang, who had heard of the Time Keepers' plans, saved Rick and summoned the Avengers to help him in his war against Immortus.
Immortus was able to invade Chronopolis with his army and use its power source to create the Forever Crystal, which he used to influence various events, like creating two versions of the original Human Torch with one of them dying, the other one becoming the android known as Vision. He also tried to prevent humanity from ever reaching into space by further manipulations, like revealing a Skrull disguised as President Nixon to the crowd (as he would've later be discovered). His revelation would cause humanity to fight aliens, which would eventually result in the tyrannic Avengers. Immortus allied himself with Yellowjacket, who promised to lead him to the Avengers in return for remaining in a timeline where he would never turn back into Hank Pym and live happily with Wasp. The two took the Avengers by surprise and led them to a trial held by the Time Keepers. They revealed their intentions of using the Forever Crystal to destroy humanity by eliminating all timelines where they went into space at all. Immortus pleaded to contain humanity instead of destroying it by using the Avengers as guards. However, the Time Keepers denied this request as it would be the Avengers who would eventually lead to the intergalactic tyranny. When Yellowjacket restored the Destiny Force to the Avengers, the Time Keepers and Immortus fled. However, with Kang's help, they followed them.
The Time Keepers ordered Immortus to use the Forever Crystal to destroy them. However, he refused due to his admiration for the Avengers, which resulted in the Time Keepers killing him and using the Crystal to summon all Avengers from every timeline where they became evil. They also decided to turn Kang into Immortus to stop the threat he was posing now, and ensure Immortus's past actions. However, Kang's firm refusal to become Immortus, which had been his main reason for fighting them all along, caused a backlash that weakened the Time Keepers, whom Kang quickly killed. Kang tried to get his hands on the Forever Crystal, but Captain America got it first and smashed it. It was then revealed by Libra that the backlash also caused the transforming Kang to split up into both Kang and Immortus, the latter bidding farewell to the Avengers and his younger/alternate self after telling them that the Crystal wasn't truly gone and would reappear eventually. After he left, Kang burst into laughter as now that a split version of him had become Immortus, it meant that he didn't have to after all.
Avengers Heroic Age
He continues in his role currently, working towards the higher purpose of keeping the timestream intact, though often using deception or murder. He does not care about morality as much in his role. He uses others to further his personal goals, as was the case when he employed the Protectorate to eliminate the threat of the Dire Wraiths. Recently, in a shocking twist of fate, Immortus was murdered by the Next Avengers. Before he died, Immortus claimed that he would be there to watch them die after he attempted to double-cross them and after killing the future Hulk and Iron Man. As Immortus has perished multiple times before and returned without much trouble, it can be assumed that this is merely another trick.
Immortus soon became an ally to the Avengers again when he became aware that his past counterpart, Kang, was meddling in the development of the Apocalypse Twins, named due to being the son and daughter of former Apocalypse heir Archangel. He'd time-nab them at the very scene of their birth, before training them to adulthood, honing their skills and influencing their minds and powers. Immortus would warn Captain America that the Twins were planning to create a mutant "rapture": kidnapping all mutants from Earth before it was destroyed by a Celestial and taking them to a new planet where only mutants would thrive. While this scheme originally succeeded after multiple miscommunications between the Avengers and the X-Men, causing Earth-X to be created (a new world where mutants and a few humans left from the original mission remained), time travel attempts by Kang would cause this event to be reversed: however, this divergent timeline would still exist, and Immortus vowed to monitor this timeline and protect it from any other altercations, either from Kang or any other beings that would attempt to do so.
Immortus would later appear with his other incarnations, Kang and Iron Lad to assist Captain America in dealing with a dysfunctional Time Gem, suspending it in an orb of "No-Time," which depowered the Gem from functioning. They stated that Captain America's attempts to deal with the Original Sin crisis would cause only disaster if allowed to continue. However, he was able to outsmart them and get to the Gem, allowing himself to time travel back to the present day.
Powers & Abilities
Immortus is immortal as a result of his service to the Time-Keepers. However, this immortality didn't seem to last forever, as he would eventually die in the far future due to old age (a sign that the Time-Keepers no longer needed him, or his moral body simply couldn't withstand the process itself). The Time-Keepers also appear to have granted Immortus control over time as well, though not to the powerful degree of Kronos. Regardless, Immortus seems nearly all-powerful, with him being able to remove timelines that don't suit him, bend time to his own will either forward, backward, or suspended, and have a near-infinite amount of Space Phantoms to use for his own ends.
Other abilities he has displayed in the past, such as energy projection or mental manipulation, may or may not be powers he has himself. Quite possibly, these powers actually derive from technology he gained during his time travels, most likely an evolved form of the technology he used while as the warmonger Kang.
X-Men: The Animated Series (1997)
During the four-parter "Beyond Good and Evil," Bishop encountered a seemingly crazy man called Bender while being trapped at the Axis of Time, which Bender claimed to be the creator of (at least that's what he thinks), spending most of the time as the janitor. The Axis was currently used by Apocalypse, who, with the aid of Mr. Sinister, Magneto, Sabretooth, and Mystique, had been kidnapping various mutants with telepathic abilities to destroy the universe by annihilating them, as he claimed that "time is motion, and motion and thought are unity." After Apocalypse was defeated in the end and all the others returned home, Bender was left commenting about the mess they caused before revealing himself to be Immortus in disguise.