My answer is: http://www.arwen-undomiel.com/images/other/Witch_king.jpg
These are the reasons why:
Lord of the Nazgul, Lord of the Nine Riders, King of the Nine Riders, the Wraith-lord, the Wraith-king, the Morgul-lord, the Morgul-king, the King of Minas Morgul, the Lord of Morgul, the Black Captain, the Captain of Despair, the Captain of Sauron, the Black Rider, the Black Shadow, the Dwimmerlaik, the High Nazgul, and the Witchking of Angmar
not to mention he fly's on a dragon and has awesome giant @$$ mace
He's completely bad @$$
not to mention the way he owns Gandalf: http://www.youtube.com/watch?v=F3VA4N1bGmA