Immortus is said to be the final incarnation of Kang the Conqueror . 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 at one point 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, 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 travelled to Limbo to finish his remaining years. 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 millenia.
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.
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 and 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 he claimed that he would be there to watch them die. What he meant by this is unclear.
Powers & Abilities
Immortus is immortal as a result of his service to the Time-Keepers. The Time-Keepers also appear to have granted Immortus control over time as well, though not to the degree of Kronos. 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.