Adam Warlock Has It
Ever since we knew that the MCU was building up to a quest for the Infinity Stones, comic book fans assumed Adam Warlock would enter the fray at some point. The heroic super-powered alien is tied into the mythos of the Infinity Gems, as they are called in the comics – in particular, the Soul Stone is housed in his forehead, much like Vision and the Mind Stone.
It didn’t look like this would happen… Until a post-credits scene of Guardians of the Galaxy Vol. 2 featured Ayesha of the Sovereign creating Adam. Director James Gunn has already played down this theory, but he would do that, wouldn’t he? As for where the Soul Stone could come into it, maybe the Sovereign’s gold skin comes from exposure to the gem?
Likelihood: Comics fans would like to believe this theory, but if Adam is going to be involved, it will be a tall ask to introduce another important character into the mix when there are already so many to juggle as it is. Then again, that’s always been the MCU way (see Age of Ultron and Civil War). The T.H.A.N.O.S. theory also holds up with this idea. In the comics, Adam is also known as Him.