The focus of the Marvel Cinematic Universe has always been the marquee superheroes at the center of each comic book blockbuster, but that's often left the villains feeling more than a little underdeveloped as a result. Of course, there've been some seriously notable exceptions to the rule, but the history of the franchise is littered with one-dimensional bad guys that have never posed a threat to a single hero never mind the entirety of the Avengers.