Complex sentence: He was a member of the progressive rock bands King Crimson and Emerson, Lake & Palmer (ELP), and recorded as a solo artist which included his 1975 hit single, "I Believe in Father Christmas".
Split into simpler sentences: He was a member of the progressive rock bands King Crimson and Emerson, Lake & Palmer (ELP). His recordings as a solo artist included his 1975 hit single "I Believe in Father Christmas".