He wowed the fashion world at the age of twenty-one, launching a career that spanned nearly five decades. In 1958, he became Christian Dior's boy-wonder successor, finding inspiration on street corners and in the canvases of modern artists. Yves Saint Laurent died yesterday in Paris, leaving behind a fashion world that still bears his indelible mark. Robin Givhan, fashion editor for the Washington Post, offers an appreciation of how his designs changed fashion on and off the catwalk.