Malekith the Accursed is the ruler of the Realm of Svartalfheim. Is he the strongest and most physically powerful Dark Elf? This concerns the comic book universe.
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No, the strongest Dark Elf of the realm of Svartalfheim was Algrim the Strong. Algrim was born over 5,000 years before the present day and served Malekith loyally through the war of the Nine Realms.
From the Marvel biography of Kurse:
Thor had fallen in love with Lorelei due to a love potion she had given him. Malekith the Accursed, to bait Thor, captured Lorelei and brought her to Svartalfheim with him. Thor being obsessed with rescuing her broke through the nexus between earth and the faerie world. When he entered Svartalfheim he saw Malekith menacing Lorelai and was distracted, and Algrim stood in ambush wearing magical ebony armor. Malekith ordered Algrim to destroy Thor and they began to battle. As the fight ensued, Malekith broke open the ground beneath them both sending them falling toward the molten lava beneath the crust of Svartalfheim. Thor summoned Mjolnir which allowed him to fly out of the pit, but Algrim sunk into the lava.
Beyonder had a fascination with Thor and wanted to test the thunder god, as a sort of science project. Sensing Algrim's hatred for Thor, Beyonder saved Algrim from death but not before the heat caused him amnesia and severe injuries. His armor had only barely kept him alive. The amnesia made him forget the true reason he fell into the lava, so Algrim seethed with rage against his last rival Thor. Beyonder restored Algrim's health and made him twice the strength of Thor as well as much better armor. At this point, Algrim the Strong became the being Kurse.
During Kurse's relentless rampage to kill Thor he found him in Manhattan. Thor donned his Power Belt which doubled his strength, making them now equal. Beyonder disapproved, so he augmented Kurse again to be vastly greater than Thor even wearing his power belt.
During battle Thor used Mjolnir to release so much intense heat and energy on Kurse that he was reminded of sinking into the lava, and his memory was restored. He now sought to kill Malekith who betrayed him.
Becoming Ruler of Hel
Unfortunately Malekith was dead, so Kurse could not kill him. Kurse rampaged past Heimdall and descended Yggdrasil the World Ash into Hel demanding Hela release Malekith so he could destroy him. Hela refused and the augmented Kurse easily bested her, becoming the Ruler of Hel himself.
Battling Thor in Full Force
Malekith was in Hel all along in the form of Lorelai (who was also dead), and in that form he decieved Kurse into believing Malekith had escaped to Midgard (Earth). He (she) also enchanted Kurse so he would see Thor as Malekith. Malekith (as Lorelai) showed Kurse the rift to Midgard, and she followed him with his army of dead in to New York, saying, "He should know he could never escape my rage merely by dying!"
The battle is partially shown below, explaining all of Kurse's augmentation.
(from The Mighty Thor #486)
This makes Kurse by far the strongest and most powerful Dark Elf; vastly stronger than Malekith the Accursed and even Thor.
Eventually Hela revealed that Malekith had been behind the whole conspiracy using Kurse to get Thor.