Who painted the Mona Lisa?

Leonardo da Vinci, probably from around 1503, and he never delivered it - he carried it with him for the rest of his life and was still working on it years later, which was entirely characteristic. He completed perhaps fifteen paintings in a career of nearly fifty years and abandoned a great many more.

The technique that makes the face work is sfumato, meaning smoked - glazes laid so thinly and blended so completely that there are no lines anywhere, only gradations. There are estimated to be dozens of layers in the face, some a few micrometres thick. The corners of the mouth are deliberately left indistinct, which is a large part of why the expression seems to change: peripheral vision picks up the shadowing as a smile and direct vision does not.

It was a well-regarded painting rather than the most famous object on Earth until 1911, when an Italian handyman at the Louvre walked out with it under his coat. The theft was front-page news across the world for two years, the empty wall drew bigger crowds than the picture had, and Picasso was briefly questioned. It came back in 1913 when the thief tried to sell it in Florence, and it has been the most visited painting in the world ever since - fame manufactured by its own absence.