Bertuccio is the Count's right-hand man. When Monte Cristo wants something done, he goes to Bertuccio, because he knows Bertuccio will carry out his orders to a tee. He buys everything from boats to houses; he keeps everything ready and waiting for use…the list goes on and on. Ultimately, though, this means nothing.
The Count really wants Bertuccio for one thing and one thing only: his history. As Haydée has the goods on Fernand, so Bertuccio has the dirt on Villefort and Caderousse. Without him, Benedetto would not have survived, and without Benedetto Monte Cristo wouldn't have been able to put Villefort out of action. As such, Bertuccio is quite possibly the biggest cog in the Count's machine.
His affinity for the Count, and his willingness to comply with his wishes becomes all too clear once he explains his family history. Like Monte Cristo, Bertuccio has a huge beef with Villefort. It seems the crown prosecutor refused to help in the search for his brother's murder. Bertuccio, being a passionate Corsican, set out to get his revenge on Villefort, eventually stabbing him in the backyard of his chateau in Auteuil. [This is where he gets to utter what are possibly the best lines in the whole book: "I am Giovanni Bertuccio! Your death is for my brother, your treasure for his widow: you can see that my revenge is more perfect than I hoped!" (44.73). He sounds a little bit like a certain character in The Princess Bride.]
Bertuccio's murder attempt puts him in a different class of avenger from the Count; like Vampa, he serves as a counterexample, and his inability to carry out the vendetta suggests that violence might not be the best way to enact retribution. In the end, control beats passion every time. As the Count tells Albert de Morcerf, "a good servant is one over whom I have the power of life and death" (85.119). Death is part of the equation, but only in the service of mastery.