Mark Rolston's most iconic role came as Bogs Diamond, predatory prison rapist and leader of the bull-fruit gang "The Sisters" in Frank Darabont's 1994 classic, "The Shawshank Redemption"; it is a role of steely, disturbing menace that has typified the actor's career. Born in Baltimore, he went to England to study acting at Drama Centre London, where he trained for five years. He returned triumphantly to the United States with the National Shakespeare Company as the lead in Shakespeare's "Richard II." A few minor appearances on television shows over the next few years led to a small part as Private Drake in the 1986 James Cameron film, "Aliens." Rolston's icy, piercing eyes made him a natural for bad-guy roles; he had turns in the sequels to "Lethal Weapon" and "Robocop." A role in the Nick Nolte prison drama "Weeds" was the precursor to his standout performance in "Shawshank," and he began a long string of intense portrayals from either side of the ethical fence on both film and television, alternating between sociopaths and law enforcement officers. He has been embraced by a new generation of fans with turns as FBI Agent Dan Erickson in the fifth and sixth installments of the "Saw" horror franchise.