Rosie Mulligan is one of Donna Sheridan's best friends and was once a member of Donna's band, "Donna and the Dynamos" as well as Donna's other best friend, Tanya, a wealthy,rich three-time divorcee. She is at first against the idea of meeting "Mr. Right" but she changes her mind completely when she meets and falls in love with Bill Anderson, a Swedish writer and adventurer and one of the three possible fathers of Donna's daughter Sophie who calls Rosie, "Auntie Rosie." In the movie, Rosie says to Tanya, "It's very Greek." She also make an appearance in Donna and the Dynamos' performance of "Dancing Queen."