The rules and powers of the Soul Stone in Avengers: Infinity War and Avengers: Endgame are vague, but the movies provide a few clues about how it really works. As Wong (Benedict Wong) explains in Doctor Strange, each of the six Infinity Stones in the Marvel Cinematic Universe is a prehistoric crystal that represents and controls "an essential aspect of existence." Thanos uses the Space Stone to teleport himself and the Black Order across the universe, the Power Stone to break a moon on the planet Titan, the Reality Stone to turn Starlord's (Chris Pratt) blaster shot into bubbles, and the Time Stone to regress Vision (Paul Bettany) back to life. The Mind Stone is known to affect the psyche, as evidenced by Vision's conscience and Loki's (Tom Hiddleston) mind-controlling scepter. But what does the Soul Stone do, and how does it work?

After years of fan speculation about what and where the last Infinity Stone could be, Infinity War revealed that it hadn't been previously set up in the MCU. Instead, the long-lost villain Red Skull (Ross Marquand) had been guarding it silently in the distant planet Vormir since the Tesseract teleported him there at the end of Captain America: The First Avenger. Skull explains to Thanos (Josh Brolin) that the Stone demands the sacrifice of that he loves the most, making it the only Infinity Stone to impose conditions and the most difficult one to collect.

Related: How Powerful The MCU’s Thanos Really Is (With & Without Infinity Stones)

After sacrificing his beloved Gamora (Zoe Saldana) and earning the Soul Stone, Thanos first combines it with the Space Stone to locate the real Doctor Strange when the wizard summons an army of clones in the Battle of Titan. The blast not only strikes Strange physically, but it also temporarily knocks the soul out of his body. This is the same role the Soul Stone plays in the Snaps, as it picks exactly half of all lives in the universe to disintegrate in Infinity War and that same amount to bring back in Endgame, demonstrating its ability to identify individual beings and possibly even to judge which to eliminate. Along with its requisite of sacrifice and its choice of Red Skull as its protector, all of this proves the Soul Stone does justice to its name, as it controls everything related to the spirit.

Another feature the Soul Stone has in the MCU is taking the user into the Soulworld, a pocket dimension that resides inside the Stone, where one meets the person who was sacrificed. When Thanos accomplishes his ultimate goal, he's transported there. Inside, he meets a young Gamora near a structure that resembles the setting of one of his fondest memories with her. Tony Stark (Robert Downey Jr.) was supposed to experience a similar moment with his daughter Morgan, played by 13 Reasons Why's Katherine Langford, but the scene was cut after test screenings. This power is also linked to why everybody that was snapped out of existence in Infinity War could be brought back in Endgame, unlike characters that died from different causes such as Vision and Black Widow (Scarlett Johansson). The Snap didn't literally kill them — the Soul Stone took them to a different plane of existence.

The Soul Stone is a vital part of Thanos's plan to wipe out half of all life in the universe in Avengers: Infinity War and also an essential part of his defeat in Avengers: Endgame. Undeniably, it's the most enigmatic part of his omnipotent gauntlet. The two movies it has appeared in have demonstrated its connection to the spiritual part of the universe, but it's obvious that there's much more to explore about it. Perhaps the upcoming Eternals will answer the remaining questions about its creation and functionality.

More: Every MCU Hero Who Got Their Powers From Infinity Stones

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