Yoda. Best mentor of all time.
(Every time I have that tweener 47 yard chip..)
But thanks to the prequel trilogy, he's easily fooled by the Sith and a coward who decided that running away and hiding was a better option than fighting a Sith lord, dooming the galaxy to generations of oppression and suffering.
Then, he comes back as a ghost and laughs at his last student's failings.
Yoda is good is theory, but man did the prequels ruin him and a lot of other characters as well.