Pop Art emerged in the mid-1950s in Britain and late 1950s in the United States. It drew upon popular art images from newspapers and TV and embraced aspects of Abstract Expressionism while focusing on realistic subject matter. Key figures included Richard Hamilton, the creator of an early Pop Art collage; Jasper Johns, known for paintings of the American flag; and Eduardo Paolozzi, a precursor to Pop Art known for using juxtaposition. Other seminal Pop Artists were Claes Oldenburg, Andy Warhol, Roy Lichtenstein, and Bridget Riley, a pioneer of Optical Art.