Mamma Mia!
Björn Kristian Ulvaeus (; 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.