Reality Stone

The Reality Stone is one of the six Infinity Stones, the remnant of a singularity that predates the universe. A force of ancient and catastrophic power, the Reality Stone has the potential to transform the entire universe. It was liquified into a dark red fluid called the Aether (pronounced ēTHər), which the Dark Elves and their leader Malekith intended to use to bring the eternal darkness upon all the Nine Realms. Taken from the Elves by the Asgardians, it was entrusted to the Collector. The Mad Titan Thanos later retrieved it from the Collector's Museum, returned its form to a Stone, and inserted it into his Infinity Gauntlet.

Origin
The Reality Stone is a remnant of one of the six singularities which existed before the universe. After the universe came into existence, four cosmic beings known as the Cosmic Entities forged the energies of these singularities into six immensely powerful objects called the Infinity Stones. This stone represents reality, as it possesses the power to bend the very laws of reality and physics, converting matter into dark matter.

The Dark Elves
The leader of the Dark Elves of Svartalfheim, Malekith, made a weapon using the Reality Stone called the Aether. Every five-thousand years, the Convergence causes the Nine Realms to become aligned. In 2988 B.C., Malekith planned to use this event to release the and plunge the nine realms into eternal darkness; however, the Asgardians intervened and took the Aether from the Dark Elves by force, watching as the race was apparently decimated in battle. Bor then had the hidden away where no one could find it, and over the following five millennia, its story faded from known history.

In 2013, near the beginning of the Convergence, a portal opened up to where the Aether was located; Jane Foster happened to walk through this portal and, through curiosity, made contact with it, causing it to become active and infest Foster's body, using her as a host. After arriving back on Earth, Foster exhibited an immensely powerful energy projection when being touched on the arm, and was taken to Asgard by Thor where the was discovered by Odin. During this time, Malekith sensed the 's activity and attempted to retrieve it by attacking Asgard. In the end, through the sacrifice of Frigga, Malekith and his army left before he could obtain the Aether.

Later though, when access to the Bifrost Bridge had been restricted, Thor, with a dying Foster, got Loki to take them through a hidden passageway to Svartalfheim. After getting there, they confronted Malekith and through various circumstances, the Dark Elf drew the Aether from Foster and into himself and left the planet. Both parties then arrived on Earth, where Malekith used the to battle Thor across worlds during the Convergence, which resulted in Malekith's destruction. Afterward, the Asgardians were able to contain the Aether, which was later given to the Collector for safekeeping, not knowing the true intentions the Collector had.

A Vision
Thor had a vision of the Infinity Stones and their role in the events of the previous years, the Reality Stone included. The Aether is shown solidifying into the Stone.

Wielded by Thanos
Years later, Thanos arrived to Knowhere and took the Aether from the Collector, solidifying it into the Reality Stone and adding it into the Infinity Gauntlet. He used it to create an illusion to trap the Guardians of the Galaxy and then briefly rendered himself invisible while talking to Gamora before revealing himself and using the Reality Stone to easily turn Drax and Mantis into pieces of matter and then transformed Quill's upcoming blast from his blasters into bubbles before warping away.

Thanos would use the Reality Stone again to turn Gamora's dagger into bubbles so he can thwart her attempt to kill herself. He later used the Reality Stone to first show Doctor Strange how Titan once was before using it offensively to a great effect when he fought half the Avengers, Guardians of the Galaxy and Doctor Strange, using it to transform the pieces of the Milano that he destroyed into swarms of black crystals when Iron Man slammed it on him, absorb an explosion and turn it into a beam of flame and even to move the Moon itself so he can use the Power Stone to crush it.

Capabilities
As the Infinity Stone that represents and governs over reality, the Reality Stone grants its user absolute control over reality itself. However, like all other Infinity Stones, due to it being the most powerful artifact in existence, it can only be wielded by beings of sufficient power and inside beings of no powers, it will inevitably kill them, as evidenced with Jane Foster. The Reality Stone's power is so great that it is capable of affecting reality on a universal scale, as Malekith would have been able to use the Stone to cover the whole universe in darkness. It is also indestructible, as not even the immensely powerful Thor wielding Mjølnir could destroy it.

Those who fully understands its capabilities can remove the Reality Stone from others and safely absorb it into themselves granted they had the necessary level of power needed, as Malekith was able to draw the Infinity Stone out of Jane and merge with it. Their physical powers are greatly enhanced, as evidenced when Malekith was on par with Thor in terms of raw strength and he was also capable of quickly regenerating lost limbs and enduring Thor's blows without any significiant damage, with Malekith only being vanquished by having his own ship collapse on him. Malekith was also able to use the Reality Stone's powers over reality to send out blasts of energy strong enough to cause Thor wielding Mjølnir trouble blocking them and harm the nearly invulnerable Asgardian and even teleport, shown when Malekith suddenly appears in front of Thor. While fully unleashing the Stone's power on the Nine Realms, Malekith also grew in size to roughly three times Thor's height.

When inserted into the Infinity Gauntlet and wielded by Thanos, it is shown that, when harnessed by a user who fully understands and masters its capabilities, the Stone is able to warp reality to a greater extent than previously perceived, as Thanos, with his strong understanding and mastery of its powers, proves able to skillfully warp reality more powerfully than Malekith's display of the Stone's power over reality, achieving numerous powerful capabilities that he very effectively employed. From the Reality Stone, Thanos acquires the power to create highly elaborate physical simulations and illusions of false realities over a wide range of influence by altering reality in said area to whatever he wished. Prior to the Ambush on Knowhere, Thanos used the Stone to create a false illusion of himself interrogating the Collector in a completely deserted Knowhere, in order to fool the approaching Guardians of the Galaxy and mask the colony's true status as burning down and utterly ruined, with it being so highly convincing that his illusionary self could physically interact with others, even able to be killed by Gamora. It seems the powerful illusionary powers the Reality Stone granted Thanos also allows him to make himself invisible, as upon unveiling the illusion, he initially talked to Gamora unseen before revealing himself. Prior to the Battle of Titan, Thanos used the Reality Stone to alter the reality around the planet Titan so as to show Doctor Strange it's former beauty in its peaceful prime, in a time before it became an uninhabited wasteland. Another powerful capability that Thanos gains from the Reality Stone's control over reality is the power to warp and transmute matter into anything he wished. While often doing this to turn and use objects in his surroundings offensively, Thanos displays that the Reality Stone's transmuting powers can even affect living organisms, as with a single blast from the Stone, Thanos easily incapacitated Guardians Drax and Mantis by temporarily warping their physical bodies, splitting Drax's body into pieces and turning Mantis into still-conscious strips of flesh, although this was at first only temporary as both eventually returned to normal. He can perform this feat with the Reality Stone even without needing to send out a blast and silently, as when Star-Lord reluctantly attempted to execute his teammate and lover, Gamora, to prevent her capture by Thanos, the Titan silently transmuted his Quad Blasters to harmlessly fire bubbles, before transforming the weapon itself into bubbles, and would later do the same to Gamora's dagger on Vormir to prevent her committing suicide. During the Battle of Titan and Battle of Wakanda, Thanos used the Reality Stone's powers very effectively in combat, transmuting a field of ship wreckage into a swarm of bats to attack Iron Man and manipulating the earth to spawn a cage of stone pillars to trap Black Widow. The Reality Stone also seems to grant Thanos the power to nullify the warping of dimensions, as Thanos was able to prevent himself from being trapped inside the Mirror Dimension by a gateway to said dimension send at him by Doctor Strange. He also appears to be able to impart immensely powerful telekinesis with the Reality Stone, able to slightly move a celestial body as large as Titan's moon so as to perfectly aim the Power Stone to crush it.

Thanos also displays that the Reality Stone can be used in conjunction with the other Stones to expand it's effects. Combined with the Space Stone, Thanos can manipulate the terrain at such a scale as to pull a flying Doctor Strange into his hand, by pulling the surface of Titan itself towards him. He was also able to use it in conjunction with the Power Stone to prevent T'Challa from using the nanites in his Panther Habit and then redirect the energy that T'Challa intended to unleash to the ground to further harden the impact when he slammed the Wakandan King.

After the Infinity Gauntlet was completed and the Reality Stone's powers reached it's full potential, alongside the other Stones, it allowed Thanos to wipe out half of all sentinent live in the universe with a simple snap of his fingers even after Thor severely wounded him with Stormbreaker. The Reality Stone's greatly enhanced powers over reality appeared to have played the role of destroying their bodies by turning them to dust.