At this point, it's pretty safe to assume that everyone knows how 'Avengers: Infinity War' ended. In a shocking turn of events which shook up the status quo of not just the MCU but of superhero movies in general, Thanos, the antagonist if not the villain, succeeds in his plan to wipe out half the universe, including a not-insignificant chunk of the main cast of heroes, and leaves the film on a cliffhanger.
But due to the nature of comics and Hollywood, it's pretty clear that the as-yet untitled 'Avengers 4' will find a way to resurrect at least most of those lost in the war and many believe, based on leaked set photos from the film, that this will be accomplished through some manner of time travel (maybe with the help of Kang the Conqueror? Maybe? Please?).
This in turn has given rise to the question: who else will 'Avengers 4' bring back? There have been a ton of important deaths already in the MCU, both onscreen and off, ranging from one-off villains to entire alien worlds, all of which could be reversed with the power of time travel. Fans speculate that in order defeat Thanos in their rematch, the Avengers will go back to resurrect their most powerful allies from their past.
While this will probably lean towards the likes of the Ancient One, Odin, Gamora, Heimdall, the Nova Corps, Zuri, Skurge, Yondu, and Quicksilver, it's entirely possible that Black Panther will make the argument that his cousin, Erik Killmonger, deserves a second chance at life. A shrewd tactician and combat specialist, Killmonger would have the strength and drive to help the Avengers against Thanos.
Another method would be if the Avengers traveled back to 1992 to acquire the valuable and extremely versatile vibranium. By interrupting Ulysses Klaue's assault on Wakanda, they could alter history so that Killmonger grows up in his father's homeland instead of America, completely shifting his ideology to make him a heroic defender of his nation.
Outside of the MCU lore, Killmonger, played by Michael B. Jordan in the cultural smash hit 'Black Panther,' is one of the most popular villains in a franchise which has often been accused of having weak or underdeveloped antagonists. Seeing him return would be a huge selling point for a film which is already guaranteed to turn a profit.