Tyrone Rugen had six fingers on one hand, and as a young man killed Inigo Montoya's father after refusing to pay the agreed price for a sword he made for him. When young Inigo challenged him to a duel, he handily defeated the boy, but let him live, scarring him on both cheeks to cure him of his "overactive sense of vengeance." Inigo then dedicated his life to taking revenge on "the six-fingered man" (he didn't know Rugen's real name.)
Years later, Rugen entered the service of Prince Humperdinck, functioning as his advisor, chief torturer, and royal inventor, who tested his devices on live prisoners on the last floor of the underground Zoo of Death (which is where the Prince recreationally hunts all manner of dangerous and exotic creatures; in the movie, there is no Zoo of Death, and the torture instead takes place in the "Pit of Despair"). His most nefarious invention was a machine that drained years of life away from its victims. This invention nearly killed Westley, the true love of Humperdinck's bride-to-be, Buttercup, whom Humperdinck had imprisoned; it drained 50 years of his life away leaving him "mostly dead". It was only through the intervention of Inigo, his sidekick Fezzik, and Miracle Max, the former royal Miracle Man whom Humperdinck had fired, that Westley's life was restored.
Inigo finally met up with Rugen during the attack on Humperdinck's wedding 'celebration', and said the words he had waited to say for twenty years: "Hello. My name is Inigo Montoya. You killed my father. Prepare to die." However, Count Rugen fled down a corridor, something Inigo had not expected at all. Rugen gravely wounded Inigo by stabbing him in the stomach with a concealed dagger, and gloated over his dying enemy as he saw the twin scars on his face and recognized him. Just as Rugen was about to deliver the fatal wound, however, Inigo recovered his strength and fought back, constantly repeating his challenge. Inigo parried two attempted deathblows relatively harmlessly into his own arms before going on the attack. He then struck Rugen with blows that mirrored those he had previously received from him, in the arms and on the cheeks. When Rugen was disarmed Inigo told Rugen to beg to offer anything that he wanted. When Rugen agreed, Inigo declared, "I want my father back, you son of a bitch!" and then killed Rugen. In the movie, these wounds occur in reverse chronological order, with the dagger strike omitted until the end - Inigo first stabs Rugen in each arm, then slashes his face, then lastly in the heart, in place of both the thrown dagger, and the grief for his father that Inigo had repeatedly articulated as a wound to the heart.