Pacino has never failed at bringing a certain level of menace to movies that were dependent on that element to ensure authenticity, and nowhere is it more clear than in the 1972 epic "The Godfather" and its two sequels.
Much of those movies' acclaim can be traced back to Pacino and his impactful performance as the core anti-hero, Michael Corleone.
Originally, Michael has no desire to be sucked into the family business (aka the mob), but over the course of the trilogy you watch with horror as Michael descends into depths of organized crime, taking over as the new boss. Spoilers for a 48-year-old movie, but Michael even organizes the killing of his own brother, Fredo, for going against the family.
Pacino's portrayal of Michael epitomized the entire "good guy, gone bad" trope in the best (i.e., compelling) way possible.