The search for the Infinity Stones is probably the closest thing to a major, overarching plot the Marvel Cinematic Universe has. The physical representations of the foundational elements of existence created during the Big Bang, each stone possesses incredible power. While the six stones don't appear in every film, they've appeared at the center of multiple entries in the franchise and are at the core of Avengers: Infinity War and the upcoming Avengers: Endgame.

But where were they before Thanos managed to collect them? Look back at the history of the Infinity Stones, as CBR charts their locations across the timeline of the MCU -- or at least, what we know so far.

Space Stone

The Space Stone wasn't initially identified as such. Instead, it was introduced as the Tesseract, first found during World War II hidden behind a mural of the Asgardian world tree (hinting that Asgardians played a role in hiding it on Earth). It was stolen by Red Skull and given to Hydra scientist Armin Zola, but Hydra lost the Space Stone when Red Skull was seemingly disintegrated and Captain America crashed the plane carrying it into the ocean. Howard Stark recovered the stone, and it ended up with the NASA/USAF joint Project Pegasus. The project, led by Dr. Wendy Lawson (secretly Mar-Vell of the Kree,) studied the Space Stone, using it to develop engines for space travel.

After Lawson's death, Carol Danvers destroyed the engine powered by those energies, which resulted in her receiving her powers. The stone was rediscovered by Captain Marvel and protected from the Kree before ending up back with S.H.I.E.L.D. Project Pegasus resumed experimentation until Loki stole the Space Stone in The Avengers and used it to open a portal for the Chituari invasion. Taken by the Asgardians in the aftermath of the battle, the Space Stone remained in Asgard until its destruction in Thor: Ragnarok. Thanos took the stone from Loki in Infinity War.

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Reality Stone

Like the Power Stone, the Reality Stone (or Aether, as it is known to the Asgardians and their enemies the Dark Eleves) was used for great destruction before being hidden away. Thousands of years ago, the Dark Eleves tried to use the stone to destroy existence, but were defeated by the Asgardians. Sealed away by Odin's father Bor after forcing the Dark Elves into retreat, the Aether remained hidden for literal ages.

But when the Convergence opened up the walls between worlds during Thor: The Dark World, Jane Foster accidentally interacted with the Aether and bonded with it. Doing so threatened Jane's life and made her a target of the Dark Elves, who eventually dragged the power out of her and fused it to their leader, Malekith.

But before Malekith could use the Reality Stone to destroy the universe, Thor and his allies were able to stop him and separate him from it. Fearful of keeping it too close to the Tesseract (reasoning that having two Infinity Stones in the same place was asking for trouble,) the Asgardians gave the Aether to the Collector. It remained there until Thanos attacked Knowhere and took it from him.

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Power Stone

The Power Stone was introduced in Guardians of the Galaxy. As revealed by the Collector, the stone was previously in the possession of the Celestials, who used it to wipe out entire planets. Others tried to harness the Power Stone but failed to contain the energies. Eventually, the stone ended up hidden on the dead planet known as Morag, inside a nondescript orb within a hidden tomb. Thanos recruited Ronan to recover the stone, but his men were unable to claim the stone before Star-Lord and the Ravagers were hired to steal it. Star-Lord made off with the stone, setting off the events of Guardians of the Galaxy.

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The group tried to sell the orb to the Collector, but when one of his servants tried to use it to strike back at her master, she was destroyed by the overwhelming power. Ronan took it and tried to use the stone to destroy the Nova Corps home world of Xandar, but the Guardians were able to band together and control the Power Stone, killing Ronan and saving the day. The Guardians entrusted the stone to the Nova Corps... who were promptly wiped out off-screen by Thanos when he attacked Xandar for the Infinity Stone.

NEXT PAGE: The Soul Stone Was Once the MCU's Best Kept Secret

Mind Stone

Like the Tesseract, the Mind Stone wasn't initially introduced as an Infinity Stone. The stone was originally in the possession of Thanos, who gave it to Loki so that he could use it to get the Tesseract. The stone was hidden within the scepter, used by Loki to take over the minds of humans such as Hawkeye and Erik Selvig. The stone, still hidden inside the scepter, ended up in S.H.I.E.L.D. custody after the events of Avengers.

But the scepter was stolen by a disenfranchised S.H.I.E.L.D. agent and Baron Strucker in the comic tie-in Avengers: Age of Ultron Prelude. The Avengers reunited in Avengers: Age of Ultron to take the scepter away from Strucker and bring down the last of the Hydra leadership. But when Ultron was created, he stole the scepter to use as part of his perfect new body.

The stone ended up becoming the lifeforce powering the being known as Vision, with the apparent consciousness inside the Mind Stone helping to form his personality. The question of what to do with the Mind Stone played out throughout Infinity War, with Scarlet Witch even destroying it at one point. But Thanos used the Time Stone to reverse the destruction and took it for himself, killing Vision in the process.

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Time Stone

The Time Stone has actually been used for good, proving essential to the protection of Earth from the dimensional conqueror Dormammu. The Time Stone was first in the possession of the ancient sorcerer Agamotto, who hid the stone within a device of his own creation. Known as the Eye of Agamotto, the tool could be used to manipulate the time stream of the entire world or even just individual moments. The Eye was kept in the mystic city of Kamar-Taj and studied by the sorcerer Cagliostro, who recorded his findings in the Book of Cagliostro.

When Doctor Strange arrived in the city, he showed particular interest in the Eye and trained with it. He utilized it against Kaecilius and his followers, reversing the ramifications of their attacks on the Hong Kong Sanctum. Strange was even able to use the stone to force Dormammu to retreat after trapping the two of them in a time loop. Strange took to wearing the Time Stone around his neck, utilizing it in Infinity War to fight against Thanos and explore what plans could help them stop the Mad Titan.

It's noticeable that he seemed reluctantly knowledgeable about the ramifications of turning the stone over to Thanos to save Tony Stark's life, hinting that he saw a path for the heroes to save the day that required half of existence to (at least temporarily) be killed.

RELATED: How the MCU's Displaced Asgardians Could Play a Major Role in Phase Four

Soul Stone

The final Infinity Stone to be introduced, the Soul Stone was hidden away from almost every force in the universe. Infinity War Prelude #2 revealed that Wong was aware of the location of most Infinity Stones, but that he had no idea where the Soul Stone was located. Not even the Asgardians knew where it was. Only Gamora found the location of the stone, eventually giving up the location to Thanos when he tortured her adopted sister, Nebula. It is not specified how the stone eventually ended up on the planet Vormir, but that's where Gamora took Thanos.

When Thanos and Gamora arrive on the planet, they learned that the Soul Stone took Red Skull (who was teleported to Vormir by the Space Stone instead of being killed as it appeared in Captain America: The First Avenger) and made him the guardian for the stone. Incapable of loving anything enough to warrant the necessary sacrifice to claim the power, the Red Skull was humbled and became a servant of the Soul Stone. He advised Thanos about the stone, and Thanos sacrificed Gamora to claim it. Taking the Red Skull as his servant hints again that the Infinity Stones seem to have something of a consciousness, but their mysterious nature means their full power is still unclear.

We'll hopefully find out more about the stones in the upcoming Avengers: Endgame. Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr., Josh Brolin, Mark Ruffalo, Tom Hiddleston, Chris Evans, Chris Hemsworth, Jeremy Renner, Chris Pratt, Elizabeth Olsen, Chadwick Boseman, Sebastian Stan, Benedict Cumberbatch, Paul Bettany, Samuel L. Jackson, Cobie Smulders, Benedict Wong, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Pom Klementieff, Scarlett Johansson, Tom Holland and Anthony Mackie. The film arrives April 26.