From his start as the owner of a kitschy poster store in Los Angeles in the 1970s, Larry Gagosian has become the most influential art dealer since Joseph Duveen. He owns 12 major gallery spaces worldwide, including three in New York. He may not be known for discovering them, but his development of contemporary artists’ careers (and particularly their markets) is unrivaled, as is his reputation for landmark exhibitions and access to the collectors with the deepest pockets. Mr. Gagosian, who has been ranked No. 1 on Forbes’s Top Ten Art Dealers list, is responsible for showcasing works by greats including Andy Warhol, Pablo Picasso and Jean-Michel Basquiat (of whom he was an early supporter). He may have lost a few artists from his roster recently—Damien Hirst, Yayoi Kusama—but he still shows big names like Richard Serra. To top it all off, he’s opening a restaurant on the ground floor of his Madison Avenue headquarters.