Mephisto
Would you believe Matt Smith as the Devil? That’s basically Mephisto in a nutshell.
He’s an extremely powerful demonic entity who likes to go around causing trouble for everyone in the Marvel universe and also has a wide range of powers – he’s immortal and he likes to acquire souls to fuel his magic by making pacts. As mentioned before, The Avengers are going to need a strong villain to fight in the future after Thanos, and Mephisto is the type of world-ending threat that could unite Earth’s Mightiest Heroes once again.
Everyone knows that playing the Devil always requires two different approaches. He should be charming and suave when he needs to be, making his demonic offers and bargains appear enticing to the weak-willed, but he also needs to be terror-incarnate when he’s angry. Anyone familiar with Smith’s work knows the actor is more than capable of handling such a role.
The best part about this character is that he fits with just about every Marvel hero and he could feasibly be inserted into just about every movie. If Matt Smith really wanted to play a villain, there should be no higher goal than Mephisto.