I was having this conversation with some of my mates after we went to see Civil War yesterday: who do you think is the best big supervillain or comic book villain? And why?
I'm putting this in the movie section, because more people are probably familiar with the movie versions of these characters than anything else. But if you want to name characters from the comic books then go ahead.
For me, the answer is definitely Magneto.
His powers are really cool, and open to being used in a lot of different ways. His motivations are understandable and even sympathetic which makes him a more interesting and fully rounded character. His love/hate relationship with Xavier adds a great dynamic to the best X-Men stories. And he really forwards the civil rights allegory that is the foundation of the X-Men universe.
The fact that he's been portrayed by two great actors in Ian McKellan and Michael Fassbender doesn't hurt either.