The Reality Stone, also known in its liquefied form as the Aether, was an incredibly powerful and ancient stone capable of manipulating reality. An Infinity Stone, various individuals have possessed it, including the Dark Elves and Malekith, Jane Foster, the Collector and Thanos. The Aether is contained within the Chamber.
Sometime prior to 2988 B.C., Malekith, the king of the Dark Elves, discovered the Reality Stone. Malekith liquefied the Reality Stone and sought to harness its power to restore the universe back to darkness. During the first Dark Elf conflict, the Asgardian king Bor buried the Aether.
In 2013, Jane Foster rediscovered the Aether and was possessed by it, reawakening the Dark Elves, culminating into the second Dark Elf conflict. Following the conflict, the Aether was given to the Collector, where it remained until 2018, when Thanos stole the Aether from the Collector. The Reality Stone was ultimately destroyed by Thanos in the wake of the Snap.