【Esther Studer】

The Esther StuderInfinity Stones have cropped up all over the MCU over the past ten years and 18 movies. But with Infinity Warapproaching, it's time to really pay attention to them.

Here's the rundown: There are six Infinity Stones (also known as gems, but they're rebranding): Time, Space, Power, Mind, Reality, and one we've never seen – Soul. When combined with the Infinity Gauntlet, they are the most powerful objects in the universe.

Five are accounted for. Time is with Doctor Strange, Space with Loki, Power with the Nova Corps, Mind with Vision, and Reality with The Collector. So where and what the heck is the Soul Stone?

1. Wakanda forever

One of the most popular theories is that the great people of Wakanda, in addition to possessing abundant stores of vibranium, are perhaps unknowingly harboring the Soul Stone – how else could they go into the spirit world at will? Now that the country has revealed its true power, the eyes of the Earth and beyond are on Wakanda – including thirsty Thanos and his obsession with the stones.

2. Look to Asgard

A rewatch of Thor: The Dark Worldwill remind us that Heimdall can see every being in the nine realms – literally 10 trillion souls, which is a lot of souls! Sounds like someone affiliated with the SoulStone, doesn't it? The stone might be connected to his orange eyes, or more likely to the gem embedded in the breastplate of his armor (though he no longer has that as of Thor: Ragnarok).

In Age of Ultron, Thor had a vision of a blind Heimdall whose sight could have been taken by Thanos in his quest for the Soul Stone. If not Heimdall, some speculate that Odin may have had the stone behind his eye patch, but the Asgardians already have one Infinity Stone and don't believe in keeping any two close together.

Yet another theory suggests the stone was encased in Thor's Mjolnir (R.I.P.) which raises the question... where is it now?

3. It's about Tony Stark (isn't everything?)

Tony couldn't be controlled by Loki's scepter, a.k.a. the Mind Stone in The Avengers, though we assumed that was because of the arc reactor. There's a moment in the teaser trailer where Tony is moving when Banner and Strange seem frozen (they might just be in shock), which would mean he isn't affected by the Time Stone either. If Tony used the Soul Stone to create his arc reactor, that would explain his body's response to the other stones.

Some have also cited a series of posters that pairs Iron Man with the Soul Stone, but in all likelihood that's because the color scheme worked out and whoever made them didn't want lil' Tony to feel left out while all his friends got their own posters.

He could still acquire it during Infinity Warand then expend all efforts (perhaps even give his life??) to protect it.

Or...

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4. It's all about Guardians Vol. 3

A popular and plausible theory is that the stone is with Adam Warlock, whom we know won't be introduced until Guardians of the Galaxy Vol. 3. The character is strongly associated with the Soul Stone in the comics, and his introduction to the MCU was teased in the end credits of Guardians Vol. 2.

And as long as we're talking about Guardians Vol. 3– the stone could as easily be with Ego, or even somehow connected to Peter Quill's human mother, Meredith. A fun crack theory is that it's with Howard the Duck, a drunk, talking waterfowl positioned close enough to The Collector, who has been known to possess more than one Infinity Stone at a time.

5. It's somewhere else entirely

Maybe we haven't seen the stone yet because Thanosalready has itand is only looking for the others. Maybe former Wasp Janet Van Dyne found it in the quantum realm and it'll be in Ant-Man and the Wasp! Maybe it actually debuts in Captain Marvel, which isn't out until 2019.

Honestly, considering that there are five other stones and approximately 9238749 characters in Infinity War, maybe this is for the best.

Avengers: Infinity Warreleases April 27.