My vote falls between 2, a Fallen Jedi and a Dark Lord of the Sith.

Revan or Plagueis

Revan? - damn what other force user loses his memories only to gain it all back in spades? and more than once...damn

Plagueis - died in his sleep..So? Achilles anyone? Seriously this guy could manipulate the force to make and unmake life...show me anyone that can be a GOD! like Plagueis..exactly