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 the 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 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 time-traveled to Vormir of 2014 to return the Soul Stone.
Guarded by Red Skull
- "A lifetime ago, I, too, sought the stones. I even held one in my hand. But it cast me out, banished me here. Guiding others to a treasure I cannot possess. What you seek lies before you. As does what you fear."
"The price. Soul holds a special place among the Infinity Stones. You might say, it has a certain wisdom."
- ―Red Skull and Thanos
As Thanos began his quest for the Stones, he sent the Black Order to scout the locations of the artifacts. Gamora and Nebula eventually tracked the Soul Stone down to Vormir only to conceal its location from Thanos with Gamora burning the map that had led them to it, though not before she had memorized its location. Thanos easily deduced that Gamora had located the Soul Stone, which he later attributed to her poor skill in lying, but allowed her to believe she had fooled him for the time being.
Several years later, Thanos revealed to Gamora that he had never been fooled by her claims of never finding the Soul Stone and managed to force her to divulge the Soul Stone's location, via ruthlessly torturing Nebula, taking her with him to Vormir. As they neared the shrine, they were approached by the 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 sacrifice allowing him to obtain the Stone.
Having successfully claimed the Soul Stone, Thanos returned to Titan, where he was confronted by an alliance of the Avengers, the Masters of the Mystic Arts and the Guardians of the Galaxy. 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 briefly 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.
- "Consider me a guide. To you, and to all who seek the Soul Stone."
"Okay. You tell us where it is, then we'll be on our way."
"If only it were that easy. What you seek lies in front of you, as does what you fear. The stone is down there. For one of you. For the other... In order to take the stone, you must lose that which you love. An everlasting exchange. A soul, for a soul."
- ―Red Skull and Black Widow
After successfully transporting the past versions of the stones to the present, Hulk, wearing a Nano Gauntlet created by Stark, harnessed the power of the six stones to resurrect the lives claimed by Thanos, albeit losing the ability to use his right arm in the process. While restoring the lives lost, he attempted to resurrect Romanoff as well, but was unable to owing to the rules of the Soul Stone. Moments after the resurrection, the New Avengers Facility was attacked by the past version of Thanos, who had time-traveled from 2014 to 2023. Iron Man, Captain America and Thor fought the Mad Titan before they were given assistance by the newly resurrected heroes, sparking the Battle of Earth, which culminated in Iron Man sacrificing his life by using all six stones to kill Thanos and his army. Following Stark's funeral, Captain America was sent back in time by Hulk in order to put back the Infinity Stones to whence they were taken and journeyed to Vormir of 2014 to return the Soul Stone.
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 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 instantly destroy all the false images and reveal 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. 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.
- 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.