Abbé Faria is quite possibly the greatest mentor ever. How else do you explain the transformation of the young, innocent Edmond Dantès into the ultimate playboy, the beautiful brilliant, learned, debonair millionaire manipulator called the Count of Monte Cristo? Seriously, the "mad" abbé takes Edmond under his wing, teaches him everything he knows, solves the mystery of Edmond's imprisonment, gives him the key to unlimited wealth and, finally, calls him his son.
And this is to say nothing of the abbé's personal accomplishments. He makes the most of his time in jail – when he's not trying to break out of it – by writing his masterwork, the Treatise on the Prospects for a General Monarchy in Italy. He, like Noirtier, is committed to his political ideals – in this case the notion of a unified Italy. He, like Noirtier, is also subject to terrible bouts of apoplexy – catalepsy if you want to pick nits – but in his case, they're fatal. Even after his death, he lives on in Edmond's heart.
It should be noted that Faria is responsible for awakening Edmond's thirst for revenge. He says as much in Chapter 17:
"I regret having helped you in your investigation and said what I did to you," he remarked.
"Why is that?" Dantès asked.
"Because I have insinuated a feeling into your heart that was not previously there: the desire for revenge." (17.93-95)
What do you think: is he's responsible for Edmond's desire for revenge? Does the good he does for Edmond ultimately outweighs the bad?