Gil Robbins, a musician and actor who was a member of the 1960s folk group the Highwaymen, died Tuesday at his home in Mexico, said his son, actor-director Tim Robbins. He was 80 and had prostate cancer. "He was very charming, open and funny," Tim Robbins told The Times on Saturday. "He had a real strong moral center; he spoke up for what he believed in." In 1962, Gil Robbins joined the Highwaymen, best known for "Michael," their recording of "Michael, Row the Boat Ashore." He spent three years with the folk group, singing baritone, writing songs and playing the guitarron, a large six-string guitar, on five albums. Before joining the Highwaymen, Robbins performed with the Cumberland Three, the Belafonte Singers and folk singer Tom Paxton.