Rugen is the right-hand of Prince Humperdinck, serving as his grand vizier. He is cruel and sadistic and has a fascination with pain, writing a book on the subject. He is the inventor of a massive torturing device that is a cross between a rack and a water pump, simply called "the Machine", that has the ability to drain years of someone's life from them.
Many years before the start of the story, Rugen visited swordsmith Domingo Montoya requesting a special sword for his six-fingered hand. When the elder Montoya completed the sword, Rugen demanded it, but at one-tenth of the original price. When the elder Montoya refused (not because of the money, but because Rugen did not appreciate the hard work invested in the weapon), Rugen slashed him through the heart. Domingo's then 11-year-old son Inigo immediately challenged Rugen. Rugen bested Inigo, but decided to leave him alive. He did scar the boy's face though.
Years later, Rugen helps Prince Humperdinck attempt to carry out his plan to incite a war between Florin and the enemy nation of Guilder, helping Humperdinck track down the wayward Buttercup, eventually succeeding at the edge of the Fire Swamp. Rugen is left to "take" Wesley back to his ship; in reality, he is ordered to take Wesley to the Pit of Despair, and Wesley immediately sees through the deception. Rugen knocks Wesley out and drags him to the Pit, where he immediately hooks him up to the Machine and sucks away one year of Wesley's life. He later asks Wesley the exact sensation he felt "for posterity"; in response to a groaning cry from Wesley, Rugen says "Interesting" and says he go as high as five years, but muses that he doesn't know what that would do to Wesley.
Later in the film, when Inigo (who now knows that Rugen is his father's murderer), Fezzik, and a revived Wesley (who was left mostly dead after an enraged Prince Humperdinck supposedly killed him after raising the Machine to the highest setting) storm Humperdinck's castle, Inigo corners Rugen and duels him again. Rugen has the upper hand for the beginning of the duel, but Inigo gradually fights back and defeats him. In a last ditch effort to save himself, Rugen tries to make it up to Inigo by offering him anything he wants. Inigo pauses to consider this, but kills Rugen, saying "I want my father back, you son-of-a-bitch."