Avengers: Infinity War is in theaters as of this week, which means the location of the last of the MCU's Infinity Stones, the Soul Stone, might be near. The Soul Stone is one of the most dangerous of the group, capable of controlling life and death in ways that even cosmic beings wouldn't attempt. It's also potentially a solution to what could be a very large body count in Avengers: Infinity War, at least if Thanos has a say about it.
So what is the Soul Stone? Historically known as the Soul Gem, this Infinity Stone has the power to steal or control actual souls. Strangely enough, the Soul Stone appears to be sentient and has often acted independently, although most of its abilities seem to requires a host body to use. It isn't exactly benevolent either, as it has a constant desire to collect souls that can only be resisted by its strongest users.
When the Soul Stone does collect someone's soul, it usually stores them within a Soul World that's seemingly inside the gem itself. The stone's user can enter Soul World at any time, but all of its other inhabitants are trapped unless the Soul Stone's user decides to help them escape. While the Soul World seems like a peaceful place to spend all of eternity, it does have some drawbacks. For one, the user of the Soul Stone can access the memories and skills of anyone trapped inside of it.
It can also affect souls in lots of other strange ways. For instance, the Soul Stone can be used to devolve someone into a more basic animal form, or reveal whether a soul is pure enough. It can also be used as a universal translator of sorts, capable of translating what other people say to its wielder and forcing others to understand what the stone's host says, mo matter what the language. Like other Infinity Stones, the Soul Stone can also shoot powerful blasts of energy, in this case capable of disrupting a person's soul and rendering them unconscious.
Traditionally, Adam Warlock has wielded the Soul Stone, and he's one of the few people who has resisted its desire to collect souls. Other past users include Thanos, Nebula, Galactus, and Doctor Strange.0comments
Right now, the Soul Stone is in the possession of Ultron. The evil robot stole the stone from Adam Warlock and used it to trap both Warlock and the soul of Hank Pym inside of it. Notably, Hank Pym's body is currently merged with Ultron, so Ultron might be able to convince heroes that he's one of the good guys as he presumably tries to collect the other stones.
In the MCU, we still don't know what the Soul Stone does or where it's located. Presumably, that will be a major plot point in Avengers: Infinity War -- or at least the upcoming fourth Avengers film -- but we'll have to wait until this weekend to find out!