[Gurthang]

Greatest? Meaning the most great in action and character I assume. In which case I would have to go with Gandalf.(uncontrollable booing from angry mob of hobbit sympothizers)

Gandalf qualities:

Wisdom: Who wouldn't have taken the Ring when it was offered? Who wouldn't have jumped at the chance to rule the world? I know who didn't.

Courage: Standing up to a Balrog to save your friends when you could just outrun them.

Trust: Leaving a simple hobbit to do a task that should take ten thousand men, knowing his odds are like...er?,well...just not good at all.

Heart: Facing legions of orcs when there is no hope.

And that's not metioning his fighting skills, his sense of humor, and his stunning good looks!