We did all the research and here it is.
The timeline and history of Kang the Conqueror in the pages of Marvel comics is more intensely convoluted than perhaps any other character, for reasons that will soon become clear. Here’s the nutshell version: the man who would come to be known as Kang was born Nathaniel Richards in the 30th century of an alternate universe designated by Marvel as Earth-6311, a reality in which the Dark Ages never happened.
According to various records of his time, he is a direct descendant of Reed Richards of the Fantastic Four, and may also be distantly related to Richards’ greatest foe, the Latverian dictator and supervillain known as Doctor Doom.
Possessed of an otherwordly, superhuman intellect, Kang employs technology which — among many, many other purposes — allows him to travel through time and in between alternate realities. There are countless versions of Kang across the multiverse, each aware of all the others, and “Kang Prime” embodies the knowledge and experience of every one of them.
He has ruled as a warlord in ancient Egypt, and as a despot in the far-flung future; he’s been known to command armies of warriors from all across time. He has taken on the Fantastic Four, the Avengers, and many more of the most powerful heroes of Earth-616 (the mainstream Marvel timeline), and if ever he is defeated, there’s always another version of him waiting to take his place.
In order to discuss all of Kang’s powers, we would have to write a novel, so just know that if the creative minds at Marvel Studios are developing their next Thanos-level threat, there would be few characters more qualified. Kang is fearless, near-unstoppable — and he lives up to his name, as a slew of galaxies and even entire realities have fallen at his hand.
Kang the Conqueror may have been set up in Avengers: Endgame
Whether purposefully or otherwise, the use of time travel as the major plot device of Avengers: Endgame could have set up the arrival of Kang quite nicely. It’s been posited that the team’s meddling in the time stream may end up having ramifications that are not yet fully understood and that the alternate timelines created in the film — like the one Captain America caused when he remained in the past, or the one created by Loki when he escaped with the Space Stone during the team’s return to the Battle of New York — might somehow give Kang the means to slip sideways into Earth-199999 (the numerical designation given to the MCU by Marvel).
For that matter, the MCU’s Kang doesn’t necessarily have to have so complicated a backstory. He could be an anonymous but brilliant scientist at Pym Laboratories or Stark Industries, inspired to tinker with time by the Avengers’ success in reversing Thanos’ snap. Or, perhaps he doesn’t exist yet in the MCU, but does in the reality occupied by whatever version of the Fantastic Four will soon make their way to Earth-199999, enabling Kang to follow. Or the fact that he’s debuting in an Ant-Man movie could mean that it’s the Quantum Realm which serves as the conduit for Kang to appear.