Marvel have been super successful with their movies for the Marvel Cinematic Universe (MCU) but one area that they haven't been so successful is their villains. They are normally forgettable because marvel focuses on the heroes more that the threat. The only exception to this is Loki, the Kingpin and arguably Red Skull, but I believe Marvel's next project Jessica Jones is introducing maybe our best villain yet. It is Zebediah Killgrave aka the Purple Man (played by David Tennant).
Dr. Zebediah Killgrave was a physician turned international spy, who was sent to infiltrate a chemical refinery. During the mission, he was doused with a nerve gas that had gave him the superhuman ability to command the wills of other people. Calling himself the Purple Man, Killgrave embarked on a criminal career.
Killgrave is a very unknown character that marvel owns and his relationship with Jessica Jones is very unique and creepy. He is pure evil. His powers are messed up, controlling his victims to do what ever he wants will makes this character hated by everyone.
If they can do to the same thing they did with the Kingpin in Daredevil he will be one of the greatest villains of all time (opinion).