3. Dormammu
Doctor Strange has all but been confirmed for Phase 3 of the Marvel Cinematic Universe and the first villain that springs to mind when most people think of the good Doctor is Dormammu. A long-standing Doctor Strange foe, Dormammu was first introduced in 1964 and is a terrifying, colossal, enormously powerful mystical entity with a flaming head, spiked armour and a flowing black cape. Everything about him is awesome. Dormammu also has ties to characters such as Loki, with whom he has formed an alliance in past comics, Hulk and Thor, whom he has battled on numerous occasions, and Odin, whom he has engaged in a game of cosmic chess, giving his character several links to the existing Marvel Cinematic Universe. Not only would Dormammu provide ample opposition for the Doctor Strange and indeed any other heroes who would dare to oppose him, he would also be a threat to the MCU as a whole - he's that powerful. He would also look absolutely amazing on screen with modern CGI treatment - his intimidating figure and flaming head would just be awe-inspiring.