Andy Warhol began as a commercial illustrator, and a very successful one, doing jobs like shoe ads for I. Miller in a stylish blotty line that derived from Ben Shahn. He first exhibited in an art gallery in 1962, when the Ferus Gallery in Los Angeles showed his 32 Campbell's Soup Cans, 1961-62. From then on, most of Warhol's best work was done over a span of about six years, finishing in 1968, when he was shot. And it all flowed from one central insight: that in a culture glutted with information, where most people experience most things at second or third hand through TV and print, through images that become banal and disassociated by repeated again and again and again, there is role for affectless art. You no longer need to be hot and full of feeling. You can be supercool, like a slightly frosted mirror. Not that Warhol worked this out; he didn't have to.