Swart is Jewish[1][2] and was born in Muiderberg, a fishing village about 20 kilometers east of Amsterdam.[3][4] His Jewish fisherman father sold herring at the market.[4][2] As a child, he and his father concealed themselves as non-Jews during the Nazi occupation of the Netherlands from 1940 to 1945, hiding from Germans and Dutch colluders, who rounded up any Jews; nearly 75 per cent of the Dutch Jewish population was killed in those years.[4]