Björn Kristian Ulvaeus (born 25 April 1945) is a Swedish musician, singer, songwriter, and producer best known as a member of the musical group ABBA. He is also the 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. He is the oldest member of the group. Björn Kristian Ulvaeus was born in Gothenburg on 25 April 1945. In 1951, he moved with his family to Västervik, Kalmar County. His parents were A…