Marlene Dumas, Mamma Roma, 2012Courtesy of Kunsthalle Bielefeld and Tate ModernWho? Before 2008, South African artist Marlene Dumas remained largely unknown beyond the realms of curators and collectors, most of her works selling for around the £50,000 bracket. But everything changed that year, when her painting The Visitor sold at Sotheby’s for £3.1m, temporarily making Dumas the world’s most expensive living female artist. Today she is widely celebrated for her abstract investigation...