Leonardo da Vinci was a genius of delay, a master of the unfinished.

Brilliant ideas swirled around him like snowflakes in a flurry and melted almost as quickly. Frustrated patrons tried in vain to get him to complete commissions, but the perfectionist wouldn’t be hurried. Unfinished work seemed to be a Leonardo specialty, and as the last decade of the 15th century dawned, he had frustratingly little to show for the prodigious talent he had displayed in his youth. “Tell me if anything was ever done,” he lamented in a notebook.

With that track record, an observer might have been dubious about the commission that came Leonardo’s way late in 1494 or early in 1495: to paint a mural of the Last Supper of Jesus and his apostles on the north wall of the refectory at the convent of Santa Maria delle Grazie in Milan.

Ross King, an English novelist and historian, tells the story, in “Leonardo and the Last Supper,” of the improbable creation of one of art’s greatest masterpieces. With a fiction writer’s feel for character, King depicts a supremely ingenious, enigmatic, stubbornly independent and underachieving Leonardo, and, with a nonfiction writer’s skill, he sets the sketch against a richly described background of a society in creative and often violent ferment.

The Leonardo who emerges in King’s pages may have been a genius, but he was a refreshingly human one. “Lacking much in the way of a formal education, he was one of history’s great autodidacts,” King writes, yet he was “a poor mathematician, often making mistakes” and had difficulty with Latin: “That one of history’s greatest brains struggled with amo, amas, amat should be a consolation to anyone who has ever tried to learn a second language.”

King judges “The Last Supper” to be “arguably the most famous painting in the world, its only serious rival Leonardo’s other masterpiece, the Mona Lisa.” That’s obviously one person’s opinion. But wherever you rank it, “The Last Supper” is an amazing work of art and King’s book a worthy account of its beginnings.