Dennis Gerrard Stephen Doherty (November 29, 1940–January 19, 2007) was a Canadian singer and songwriter. He was most widely known as a founding member of the 1960s musical group The Mamas & the Papas. Dennis Gerrard Stephen Doherty (November 29, 1940–January 19, 2007) was a Canadian singer and songwriter. He was most widely known as a founding member of the 1960s musical group The Mamas & the Papas.