Malekith the Accursed was the leader of an ancient race known as the Dark Elves.
Before the Universe began, Malekith and the Dark Elves were at war with Asgardian forces lead by King Bor. Malekith tried to possess the Aeither but was provoked by Asgardian soldiers who stalled him into buying enough time for the Aeither to be teleported. Malekith and Algrim left Svartalphiem in hopes of retrieving the Aeither one day.
After Jane was exposed to the Aeither, Malekith and his remaining forces reawaken and set out to retrieve it.