The Soul Stone was unique among the Infinity Stones in Avengers: Infinity War and Avengers: Endgame, as it required a sacrifice of someone close to any who would possess it. However, in the films’ early planning stages, the stone was nearly created as something else entirely: Captain America himself.
“Early on in development talks we considered making Cap the soul stone,” the Russo Brothers posted on Twitter when asked if any consideration had been given for a different location for the stone besides Vormir. “But that idea fell away rather quickly.”
The idea of making the Soul Stone an actual person, let alone a founding member of the Avengers, would certainly have been unique. A distant relation to that notion instead made it into the final films, where Johann Schmidt, Cap’s former enemy The Red Skull, was revealed to be an ethereal spirit serving as the stone’s guardian.
In Infinity War, Thanos encountered Schmidt, and per his edict, sacrificed his adopted daughter Gamora to claim the stone. In the altered continuity of Endgame, Clint Barton and Natasha Romanoff battled one another to serve as the sacrifice so that the other could claim it. Clint was the eventual survivor.
In comic book continuity, Adam Warlock possessed the Soul Gem before his own soul became a part of it.
Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr. as Iron Man, Chris Evans as Captain America, Mark Ruffalo as Bruce Banner, Chris Hemsworth as Thor, Scarlett Johansson as Black Widow, Jeremy Renner as Hawkeye, Brie Larson as Captain Marvel, Paul Rudd as Ant-Man, Don Cheadle as War Machine, Karen Gillan as Nebula, Danai Gurira as Okoye and Bradley Cooper as Rocket, with Gwyneth Paltrow Pepper Potts, Jon Favreau as Happy Hogan, Benedict Wong as Wong, Tessa Thompson as Valkyrie and Josh Brolin as Thanos.
The Soul Stone was unique among the Infinity Stones in Avengers: Infinity War and Avengers: Endgame, but the original plan was even more different.