The Aether is a mysterious force that existed before the birth of the Nine Realms. It is known to be able to convert matter into dark matter, and otherwise maintains an almost lifelike existence that causes it to bond in a parasitic fashion to a living host. Once bonded, the energies of the Aether slowly consume the energy of any mortal host, and also have a volatile and deadly effect on any who come into contact with the host in a manner that the Aether perceives as threatening. Bonded with a stronger host that understands its power, the Aether can be employed as a weapon where it lashes out with a concussive force, or reaches out to convert matter. During its brief time bonded to Malekith, the only one who fully understood its capabilities, it was capable of creating tendrils of itself to strike out at opponents, or even regenerating lost limbs, along with creating a tornado of Aether energy. Whilst bonded to Malekith, the Aether greatly enhanced his physical strength and durability thereby allowing him to fight Thor on a reasonably even basis. On its own, the Aether is capable of sending out pulses of power that can throw back any who it deems a threat to itself. The Aether appeared to have a connection to Malekith and the Dark Elves in that it awoke them from hibernation and drew them to Asgard, as well as providing its human host with the ability to sense the former's presence.
Every five-thousand years a cosmic event known as the Convergence causes the Nine Realms to become aligned, and Malekith planned to use this event and release the Aether to plunge the Nine Realms back into darkness. But the Asgardians intervened and took the Aether from him by force. Bor then had it hidden away where none could find it, and over the following five millennia its story faded from known history.
After five-thousand years, the next Convergence brought the Nine Realms into alignment again, and in so doing portals began to appear in the walls between realms. Jane Foster was dragged through one such portal to the hidden vault of the Aether where it bonded itself to her. After arriving back on Earth, Jane exhibited an immensely powerful energy projection just by being touched on the arm. Took arrived on earth and took Jane to Asgard for treatment, but the physicians there could do nothing to remove it. During this time, Malekith had sensed the Aether's activity and attempted to retrieve it by attacking Asgard. In the end, through the sacrifice of Frigga, Malekith and his army escaped from Asgard before he could obtain the Aether.
The Aether quickly became the central focus of a war when Malekith returned after a five-thousand year sleep to reclaim it. He almost succeeded when he pulled the Aether from Foster into himself and became its new host, but was stopped in the act of transforming the Nine Realms by the combined efforts of Foster and Thor. Both parties then arrive on Earth, where Malekith uses the Aether to battle Thor across worlds during the Convergence until eventually Malekith is killed.
Having recovered the Aether, Sif and Volstagg decided that it was unwise to store two Infinity Stones in one vault, and so they turned the Aether over to Taneleer Tivan, the ageless archivist and curator known as "the Collector", for safekeeping.
