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- Malekith the Accursed - The ruler of the Dark Elves, one of the Nine Worlds of Asgardian cosmology.
- Mangog - He is the sum total of the hatred of a billion billion beings that were once killed by the ruler of Asgard. Imprisoned deep beneath Asgard, Mangog is accidentally freed by the Rock Troll Ulik, and seeks to destroy Asgard.
- Megatak - An industrial spy. He was inside an experimental video display when he gained his powers.
- Mephisto - A demon who rules another dimension and has clashed with Thor on different occasions.
- Mercurio the 4-D Man - Alien with the ability to generate flames from the right hand and extreme cold from the left.
- Midgard Serpent - A monstrous creature large enough to coil round the Earth whom Thor is destined to battle during Ragnarök.
- Mister Hyde - Amoral doctor turned rampaging strong man when he takes a potion he invented and former partner of Cobra.
- Mongoose - Probably a real mongoose before his powers were genetically engineered by the High Evolutionary to serve as his agent.
Read more about this topic: List Of Thor Enemies