The brilliant British painter George Stubbs knew horses inside out. He spent a year and a half dissecting equine carcasses for his Anatomy of the Horse (1766), a book that made him famous throughout Europe. He knew the overwhelming physical grace and beauty of horses, as in this portrait of a bright-eyed Thoroughbred racehorse named Molly Longlegs, each muscle of whose long legs is depicted with anatomical accuracy. He knew their very souls; looking at his portraits of horses, one has the uncanny sense that Stubbs has penetrated their private inner worlds. Stubbs was the greatest horse painter of all time. But to call him a horse painter is a bit like calling Cézanne an apple painter. He managed to unite in his paintings the dominant strands of the Enlightenment, balancing scientific observation with aesthetic surprise. In the process, he found ways to refresh Neoclassical traditions of order and decorum, based on Greek and Roman models, with a new Romantic spirit of passionate and sometimes violent emotion. Horses were his starting point, but as the Frick exhibition on the bicentennial of his death shows, it is where Stubbs went from there that makes him the most intriguingly complex British painter of his generation.