Björn Kristian Ulvaeus (Swedish pronunciation: [ˈbjœːɳ ɵlˈvěːɵs] (listen); born 25 April 1945) is a Swedish singer-songwriter, producer, a member of the Swedish musical group ABBA, and co-composer of the musicals Chess, Kristina från Duvemåla, and Mamma Mia! He co-produced the films Mamma Mia! and Mamma Mia! Here We Go Again with fellow ABBA member and close friend Benny Andersson.