Darth Vader. As a icon of perfect evil, he was ideal, using mystical powers to choke to death bearers of bad news, betraying his mentors, towering in black over his minions. Then comes the act of redemption. Do you think you could find anyone even slightly into movies who would not recognize the character and have an opinion?
Second vote would be Harry Potter, but he was a book character before a movie character. If we opened that up, the list gets a lot bigger.