There are so many secrets surrounding “Avengers: Infinity War,” but one of the biggest is the location of the Soul Stone. The film’s villain, Thanos, has been searching for the Infinity Stones for years, and while viewers know where the others are located, the Soul Stone remains a mystery. However, there are several theories about the elusive MacGuffin.

T.H.A.N.O.S. This has been a common theory for a while now. The Infinity Stones introduced so far could spell out Thanos’ name. T is for Tesseract (which holds the Space Stone). A is for Aether (the Reality Stone). N is for Necklace (the Time Stone is in a necklace). O is for the Orb (which holds the Power Stone). S is for Scepter (which held the Mind Stone until Vision was born).

The only letter missing is H. Heimdall’s (Idris Elba) orange eyes have made fans think he has the soul stone. The heart-shaped herb from “Black Panther” is also a contender.

Thanos Soul Stone
Will the Infinity Stones actually spell out Thanos' name in “Avengers: Infinity War”? Marvel Studios

Wakanda While director Ryan Coogler said he didn’t want to introduce the Soul Stone in “Black Panther,” that doesn’t mean he didn’t show it. There are theories that the heart-shaped herb could be the Soul Stone. However, others believe it could be the orange sand that each new king is buried in. The process with the herb and the sand allows one to speak to dead ancestors, which makes both guesses plausible.

Of course, the Soul Stone could also be something that has yet to be seen (keep in mind that the Infinity Stones typically don’t appear as plain gems). What we know for sure is that Thanos is bringing his army to Wakanda, and that doesn’t seem like a random choice.

Captain Marvel: The 2019 origin movie takes place in the 1990s, so that means Carol Danvers already exists and is pretty powerful in the present. She could be holding onto the last Infinity Stone. Brie Larson is reportedly making her debut as female hero in “Avengers: Infinity War,” so it would be possible.

Infinity War Soul Stone
Doctor Strange has the Time Stone, but could Iron Man have the Soul Stone? Marvel Studios

Tony Stark: There are some fans who believe Iron Man (Robert Downey Jr.) is the Soul Stone. According to ComicBook.com, fans believe that Howard Stark made Tony from the Soul Stone. In “Iron Man 2,” Howard calls his son his “greatest creation.” Theorists also believe Howard’s desire to have a child late in life is questionable. He was so focused on his work that it might make more sense if having a child was an experiment.

Others theorize that the arc reactor is somehow holding the Soul Stone, but Tony isn’t exactly a Celestial. This seems like the least likely situation.

Thanos Has It: All of these theories are based on the idea that Thanos has no Infinity Stones at the beginning of “Avengers: Infinity War.” The reality is, no one knows if that’s true. He’s been searching for them for years now. It actually seems unlikely that he’s starting off with an empty gauntlet.

Fans will find out where the Soul Stone is when “Avengers: Infinity War” hits theaters April 27.