Björn Ulvaeus is a Swedish musician and producer. He is best known as a member of ABBA with Benny Andersson and Anni-Frid Lyngstad. He co-produced the ABBA-based musical films Mamma Mia! (2008) and Mamma Mia! Here We Go Again (2018). Before ABBA, Ulvaeus joined the Swedish band Hootenanny Singers. He released solo singles in the late 1960s, made multiple joint albums with Andersson including Lycka, and produced two Gemini albums. Ulvaeus has appeared in the documentaries ABBA: Super Troupe and Abba Forever: The Winner Takes It All, and in the mockumentary film ABBA: The Movie.