Pop Art began in the 1950s in London as a reaction against abstract expressionism. It focused on mass production and popular culture by using images and objects from advertisements, comics, and everyday culture. Some of the most influential pop artists included Andy Warhol, who produced iconic pop images of celebrities and consumer goods, Roy Lichtenstein, known for his comic book-inspired works, and Robert Rauschenberg, a pioneer of combining diverse media into "combines." Pop Art spread to the United States and represented lighthearted popular themes through techniques like duplication and serialization.