Karin Elisabeth Dreijer (born 7 April 1975) is a Swedish singer-songwriter and record producer. Dreijer was one half of the electronic music duo the Knife, formed with their brother Olof Dreijer. Dreijer released, under the alias Fever Ray, their self-titled solo debut album. It was released digitally on 12 January 2009 and physically on 18 March 2009 through Rabid Records to universal acclaim. The album was preceded by its lead single "If I Had a Heart" (2008), which was used in numerous television series, including Person of Interest, Breaking Bad and Wentworth, as well as the opening theme song for the Canadian-Irish historical drama television series Vikings.