Björn Kristian Ulvaeus (credited as Björn Ulvæus ['bjœ?? ?l've??s] (listen); born 25 April 1945) is a Swedish 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 film Mamma Mia! with fellow ABBA member and close friend Benny Andersson.