Björn Ulvaeus was a part of a Swedish pop group, formed in Stockholm in 1972, as well as co-producer on the film "Mamma Mia!" with who?
ABBA: ABBA (] ) were a Swedish pop group, formed in Stockholm in 1972 by members Agnetha Fältskog, Björn Ulvaeus, Benny Andersson, and Anni-Frid Lyngstad. Björn Ulvaeus: Björn Kristian Ulvaeus (] ) (born 25 April 1945; credited as Björn Ulvæus) is a Swedish songwriter, producer, a former member of the Swedish musical group ABBA (1972–1982), and co-composer of the musicals "Chess", "Kristina från Duvemåla", and "Mamma Mia!
i don't know