The Soul Gem was one of the Infinity Gems, green in color, able to tap into the spiritual energies of the universe. It is also capable of stealing the souls of living beings, though Adam Warlock, its most famous wielder, used this ability sparingly. Those souls it absorbed were taken into the Soul World, a pastoral pocket universe contained within the Gem.
The Soul Gem was intelligent, generally controlling the being that wore it, and it went through hundreds of hosts. Eventually, however, it was taken into the possession of the High Evolutionary, who was too clever to allow the Gem to dominate him. The Evolutionary kept it in storage for years, but eventually gave the Gem to Warlock, who was too strong of mind to control. Warlock used the Gem to defeat the evil Man-Beast's attempt to conquer Counter-Earth, and many other feats, before he died battling Thanos. During that time, Warlock took the souls of his dying friends Pip the Troll and Gamora into the Soul World, and entered there himself as he died.
The Gem was next passed to the In-Betweener, who made little use of it, until Thanos returned from the dead and took it from him. Now part of the Infinity Gauntlet, Adam Warlock, Gamora, and Pip were able to leave the Soul Gem and inhabit the bodies of three newly-dead humans, which soon transformed into replicas of their original forms. Using his rapport with the Soul Gem, Warlock was able to take control of the entire Gauntlet, claiming it for himself.
After Eternity was able to convince the Living Tribunal to prevent the Infinity Gems from being used together, Adam Warlock took the Soul Gem for himself. He gave the rest of the Gems to his Infinity Watch. Following the pilfering of the Infinity Gems by Rune, the Soul Gem was lost with the others somewhere in that entity's native universe, prompting Adam Warlock to search for it. He has been at this task ever since.
Among the various Infinity Stones, the Soul Stone was said to be unique as it operated as a kind of hard drive with it being vast and possibly limitless device for information. (All-New Guardians of the Galaxy v1 #10)
With Devondra defeated, the heroes sought to restore the universe yet keep Warp World and its inhabitants still alive. Thus, they copied Warp World and its inhabitants who were placed inside a facet of the Soul Stone. They then departed as Devondra’s world collapsed and was destroyed as the universe was restored. Adam Warlock later imbued the stone with a souls alongside the other gems in an effort to stop conflict from spiralling over ownership of the cosmic relics. Each of the stones departed as they made their own choices on their respective destinies with Warlock intending to keep the Soul Stone as he had a special relationship with it. However, the gem like its compatriots decided to also depart into deep space. (Infinity Wars v1 #6)
- The Soul Gem was created by Roy Thomas and Gil Kane where it made its first appearance in Marvel Premiere v1 #1 (April, 1972).
- Prior to Thanos' identification of each Infinity Gems' properties, they were all called "soul gems."
- All-New Guardians of the Galaxy v1: