Like many artists of his era, Richard Diebenkorn fought in World War II and then went to school on the G.I. Bill. He attended California School of Fine Arts (a school where he later taught). In addition to landscapes like the piece here he also did extensive figurative work and apparently had a fascination with heraldry.
Kiefer is a post-war German artist whose work is, at least in part, drawn from his generation's rejection of Germany's past. He takes images that are the sort of thing you might associate with German chauvinism and casts them in a critical light. Kiefer lives and works in France.
Bates, from the great state of Texas, often paints on bronze and aluminum. This piece is a more traditional work on canvas. His work is elegant, intricate and is held by numerous prestigious museums (Corcoran Gallery of Art, Whitney Museum of Art, Hirschorn, San Francisco Museum of Art and many others).
Be sure to head to the Berggruen website. Unlike many they provide lots of information on their artists and works.