George Martin Duke (January 12, 1946 – August 5, 2013) was an American keyboardist, composer, singer-songwriter, and record producer. Throughout his career he worked with musicians like Frank Zappa. George Martin Duke (January 12, 1946 – August 5, 2013) was an American keyboardist, composer, singer-songwriter, and record producer. Throughout his career he worked with musicians like Frank Zappa.