The Soul Stone was one of the six Infinity Stones, the remnant of a singularity that predates the universe. For some time, it was kept on the planet Vormir under the watchful eye of Red Skull, before Thanos came to the planet in search of it and had to tragically sacrifice his beloved daughter Gamora to obtain it.
In 2023, the Avengers initiated a Time Heist in order to resurrect the lives Thanos had claimed, with Hawkeye and Black Widow sent back in time to an alternate 2014 to retrieve the Soul Stone from Vormir, with Romanoff sacrificing her life. Following the Battle of Earth, where Iron Man used all six stones to kill Thanos and his army at the cost of his own life, Captain America returned the Soul Stone to 2014.
The Soul Stone is a remnant of one of the six singularities which existed before the universe's creation. After the universe came to be, the Big Bang forged the remnants of these singularities into six elemental crystals, dubbed the Infinity Stones, and hurtled them across the universe. The Soul Stone represented the soul. It would later go on to cultivate a reputation of mystery throughout the galaxy. Even those who were well versed in the powers, and even locations, of the other five Stones, had little concrete knowledge regarding the Soul Stone to the point of only knowing its name. Despite, or perhaps because of, this aura of mystery, it would eventually be considered as the most dangerous of all the Infinity Stones. Even the Asgardians knew little of the stone, with Thor stating no one had ever seen it or knew where it was.
Guarded by Red Skull
The Soul Stone eventually found its way to Vormir where it became concealed in a shrine, accessible only to those who were willing to sacrifice someone that they loved. In 1945, the Space Stone banished Red Skull to the planet after he had abused its power, due to knowing that the HYDRA commander would be unable to make the sacrifice required to obtain the Soul Stone. The Soul Stone then cursed Red Skull, transforming him into an immortal wraith with the power to immediately know whoever comes to Vormir and preventing him from leaving the planet. He eventually would go on to accept this fate, become a Stonekeeper and serve as an adviser to those who would seek the Soul Stone's power.
Acquired by Thanos
In 2018, Thanos had captured Nebula and accessed her memory drive, discovering that Gamora knew the location of the Soul Stone. Forcing her to divulge the Soul Stone's location by torturing Nebula, the pair traveled to Vormir. There, they were approached by Red Skull who explained that Thanos had to sacrifice someone he loved in order to gain the Stone. Thanos then tearfully threw Gamora off of the cliff, her sacrificial death allowing him to obtain the Stone.
Having successfully claimed the Soul Stone, Thanos returned to his desolate homeworld of Titan, where he was confronted by an alliance of Doctor Strange, the Avengers and the Guardians of the Galaxy. Upon breaking free from being restrained, Thanos used the Soul Stone to remove the souls from the Guardians. When Doctor Strange cast a spell creating dozens of copies of himself in order to restrain him, Thanos used both the Soul Stone and the Power Stone to track down the real Strange and destroy the copies.
Thanos then headed to Wakanda, where he retrieved the Mind Stone from Vision. Although he was stabbed by a vengeful Thor, Thanos retained enough strength to complete his quest, activating the Infinity Gauntlet with all the Infinity Stones, including the Soul Stone, to wipe out half of all life in the universe. This act briefly sent his consciousness into the Soulworld, where he communed with a reflection of Gamora in her child form, telling her that he had achieved his goal but solemnly admitting that fulfilling his destiny had cost him everything.
Alternate Universe Versions
In 2023, the Avengers initiated a Time Heist, where they used time travel to acquire all six Infinity Stones from different points in time in order to resurrect the victims of Thanos' Snap. Arriving in an alternate 2014, Black Widow, Hawkeye, Nebula and War Machine used the Benatar to travel to Morag and Vormir. While on Vormir, Romanoff and Barton met Red Skull, who informed them that one would have to sacrifice the life of a loved one in order to obtain the Soul Stone. Despite Barton's attempts to sacrifice his own life, he was bested by Romanoff, who fell off the cliff, thereby allowing Barton to acquire the stone. While mourning Romanoff's death, Barton used the Quantum Realm to return to his timeline.
After successfully transporting the past versions of the stones to their timeline, the Soul Stone was placed in the Nano Gauntlet. Using the gauntlet, Bruce Banner harnessed the power of the six stones to resurrect the victims of the Snap, albeit losing the ability to use his right arm.
In the culmination of the Battle of Earth, the six stones were used by Tony Stark to kill an alternate Thanos and his army. Following Stark's funeral, Steve Rogers was sent back in time by Banner in order to put back the Infinity Stones to whence they were taken and journeyed to the alternate 2014 to return the Soul Stone.
Seized by the TVA
The Soul Stone ranks as possibly the most dangerous of all the Infinity Stones, with it holding a special standing among the others. Uniquely, in its shrine on Vormir, the Stone purposefully imposed a test to those who would try to claim it - only the sacrifice of a loved one to the Stone would allow for someone to wield it. The sacrifices for the Stone are permanent and irreversible, as not even the nigh-omnipotent combination of the Six Stones could resurrect them. The Soul Stone has the ability to manipulate the soul, the essence that makes up an individual, and has the ability to resurrect and conjure the spiritual representation of the people who are dead.
Upon Thanos acquiring it, the Titan uses it the least out of all the Stones but still displays familiarity with the Soul Stone's powers. During the Battle of Titan, when cornered by Doctor Strange's mirror images, Thanos activated the Soul Stone and combined it with the Power Stone to locate Strange's soul, destroying all the false images in the process and revealing the real one while also briefly forcing Strange's astral form out of his body.
After the Infinity Gauntlet was completed, the Soul Stone was used in tandem with the five other Infinity Stones to wipe out half of all life in the universe with Thanos' Snap.
- In the comics, the orange-colored (previously green) Soul Gem gives the owner the power to alter and manipulate all souls. It also acts as a gateway to its own pocket dimension. When used in conjunction with the other gems, it gives the user complete control over all life in the universe.
- The Soul Stone contains a pocket dimension, consisting entirely of shallow water underneath a dim orange sky, where the souls of the dead can be communicated with. Apparently, the subconscious of the stone’s wielder determines the Soulworld’s environment once it is entered, as in Thanos’ usage, a younger version of Gamora standing underneath an archway appeared, whereas in Iron Man’s, there appeared a small tree and a tent, along with an older version of Morgan Stark, although this particular scene was cut out of the final copy of the movie.
- The Soul Stone is the only known Infinity Stone that seemingly can be wielded by anyone, as Hawkeye despite being a normal human was able to hold the Soul Stone. It's possible that due to its unique nature, it doesn't recognize its user as being worthy based on their power but more on their understanding of the power the Soul Stone holds, meaning that as long as they have sacrificed someone they loved for the stone and thus fulfilled the requirements, they can use the Soul Stone.
Behind the Scenes
- According to Anthony and Joe Russo, they had considered making Steve Rogers the living incarnation of the Soul Stone.