Taskmaster
One of Marvel’s most formidable villains deserves an actor like Matt Smith playing him. Taskmaster is a unique antagonist with the power to absorb knowledge instantaneously, which means he can mimic almost any fighting style or talent used against him. If he watches Black Widow do some crazy kung fu, he’ll instantly know how to do it as well. If he watches Hawkeye use a bow and arrow, he’ll become an expert, too. If he sees Captain America somehow defy the laws of physics with his super shield throwing power, Taskmaster will also be able to do it.
As cool as the villain is, there’s also something a little tragic about his power. The more knowledge he learns instantaneously, the more of his own memories get erased, which would create a degree of sympathy for a character that’s generally perceived as villainous. He isn’t super-powered enough to be the “Big Bad” of a film, but he’s a more than worthy henchman who could give our heroes an incredibly difficult time.
And for some reason, if Marvel didn’t want to cast Taskmaster as a villain, there’ve been times where he’s been painted as more of an antihero, which adds another dimension to his already interesting character. Smith would be an exciting choice for the role and casting him would go a long way in making Marvel villain henchmen more dynamic.