Imagine presents a portrait of the artist regarded by many as the greatest painter of all time. Court painter to Philip IV of Spain, Velazquez is the artist other painters most admire, and his masterpiece, Las Meninas is considered the high point of European Art - yet he virtually abandoned his art for material gain and social ambition. Alan Yentob travels to Seville, Madrid, Rome and New York to meet artists and critics who add more to the story of Velasquez's genius