Dormammu

Recommended Reading
Strange Tales v1 #126-127 (First appearance)

Strange Tales v1 #130-146 (The eternity saga)

Avengers v1 #115-118 (Avengers / Defenders War)

Defenders v1 #8-11 (Avengers / Defenders War)

Dr. Strange v2 #6-9

Dr. Strange v2 #49-51

Dr. Strange : Sorcerer Supreme v1 #1-2

Defenders : Indefensible #1-5