Greatest?
I would have to give it to either Lelouch, Light, or Spike, particularly in that order.
Honorable mention to Obito as well (People might bash me for this, but it's not based on likability. Obito is an amazingly created and developed character for the story. His symbolically created characterization represent the majority of conflict-based themes in the manga, which no other character does alone in my opinion. Seriously, Obito is an incredible character for the manga.)