Malekith is a supporting antagonist of the Marvel Cinematic Universe, appearing as a major antagonist of Phase Two and a posthumous antagonist in Phase Three. He is the main antagonist of Thor: The Dark World, a posthumous antagonist of Thor: Ragnarok, a posthumous antagonist of Avengers: Infinity War and a posthumous antagonist of Avengers: Endgame.
Thor: The Dark World
Malekith is the leader of the Dark Elves who seeks to plunge the Nine Realms into darkness using the Aether. He is first seen battling Odin's father, Bor, and his Asgardian forces when he attempts to unleash the Aether. Bor is victorious, which forces Malekith and his Dark Elves to retreat into suspended animation, until the Aether is found and bonded with a host.
Thousands of years later, Dr. Jane Foster accidentally stumbles upon the Aether and becomes bonded with it; this awakens Malekith and his army. Sensing the Aether's power, Malekith hatches a plan to get his weapon back. After being infected by the Aether, Jane is transported to Asgard by Thor for treatment; sensing this, Malekith gives his lieutenant, Algrim, a Kursed stone and secretly plants him with prisoners being transported to Asgard's holding cells. After Algrim uses the stone to turn into the powerful warrior Kurse, he breaks free of his cell and manually drops Asgard's defenses, allowing Malekith and his army to invade the realm unhindered.
Once within the halls of Odin's kingdom, Malekith and Kurse seek out Jane; however, Frigga, Thor's mother, defends Jane and briefly fights Malekith, resulting in her death at the hands of Kurse. An enraged Thor attacks the pair of Dark Elves, gravely wounding Malekith before they are both able to escape to their home realm Svartalfheim, where Malekith is placed in a healing chamber. Eventually, Thor and Loki, along with Jane, track down Malekith to Svartalfheim. Once the three of them arrive, Malekith is able to sense the Aether within Jane and leaves his ship to meet Thor.
After Loki seemingly betrays Thor and hands over Jane, Malekith proceeds to extract the Aether from Jane, only for Thor and Loki to quickly reveal that the betrayal was only a ruse so Thor could attempt to destroy the dark weapon with his hammer Mjolnir. The Aether, however, quickly reassembles itself, and it is subsequently ingested by Malekith himself. Malekith then leaves for London to complete his plans to bring darkness to the realms while Kurse stays behind to battle Thor and Loki, but is killed, seemingly at the cost of Loki's life.
Malekith arrives in London, where he is greeted by Thor. The two then duel, with both being an even match for the other. Eventually, a portal separates the two during battle, leaving Malekith on Earth and Thor in Svartalfheim. Malekith, unopposed, begins to unleash the Aether's full power; however, Thor is able to return to Earth using another portal and a tube train in time to stop the Dark Elf.
During their final battle, Thor uses Dr. Eric Selvig's portal devices to impale Malekith through the chest, which after activating sends him back to Svartalfheim. The Aether shuts down, and Malekith's ship begins to crumble and fall into the London streets on Thor and Jane, only for Selvig to use another one of his portal devices to send the falling ship into Svartalfheim and crashing into a wounded Malekith, finally killing the Dark Elf for good.
He is portrayed by English actor Christopher Eccleston.