Dormammu

Dormammu is a demon of flame that exists in a realm called the Dark Dimension. He considers himself as the ruler of humanity.

Hulk and the Agents of S.M.A.S.H.
Dormammu and his army of Mindless Ones attempted to break through the barrier between Earth and the Dark Dimension. He caught Doctor Strange, but lost in a battle between him and Doctor Strange, A-Bomb and Hulk. He instead hide in Doctor Strange amulet and escaped in to the real world but defeated by the Agents of S.M.A.S.H., the house and Doctor Strange. Dormammu is consider to be one of Dr. Strange's toughest enemies.

Ultimate Spider-Man
Dormammu placed a spell upon the superhero Cloak to take control of him. With Cloak at his command, he used his teleportation powers to capture various mystics to be placed under his control. After kidnapping White Tiger and Iron Fist, he had Cloak capture Doctor Strange and confiscated a crystal called the Siege Perilous from Strange to open a portal strong enough to enable his army passage to Earth, and subsequently had them all placed under his control. However, his plan is hampered when Spider-Man and Cloak's partner Dagger free Cloak from the spell and eventually White Tiger and Iron Fist.

Unfazed by this turn of events and with the Siege Perilous fully charged, Dormammu has Doctor Strange aid him against extinguishing the heroes which proves fruitless for the heroes due to Dormammu's nigh invulnerability in the Dark Dimension. However, Cloak and Dagger manage to break the control over Doctor Strange who is able to injure Dormammu as the group escapes with the Siege Perilous in hand. When the group tries to escape through Cloak, Dormammu halts Cloak and uses him to enter Earth. But just as he arrives, Dormammu is rendered vulnerable and is banished back to the Dark Dimension by the combined powers of Spider-Man and Doctor Strange.