Amanda Michelle Seyfried (pronounced /ˈsaɪfrɪd/ "sigh-frid"; born December 3, 1985) is an American actress and former child model. She is best known for her roles as Sophie Sheridan in the feature film Mamma Mia! and as Karen Smith in Mean Girls; she has also appeared in Alpha Dog and in the television shows Veronica Mars, Big Love, and House.She is attached to star in the film version of A Woman of No Importance and Gary Winick's Letters To Juliet.