Complex sentence: Holbrook initially gained notoriety for a one-man stage show he developed while in college in 1954, performing as Mark Twain, and made his film debut in Sidney Lumet's "The Group" (1966).
Split into simpler sentences: Holbrook initially gained notoriety for a one-man stage show he developed while in college in 1954, performing as Mark Twain. He made his film debut in Sidney Lumet's "The Group" (1966).