"On August 21, 1911, an amateur painter set up his easel near the spot where Leonardo da Vinci’s “Mona Lisa”—one of the most famous works of art in the world—hung in the Louvre. To his surprise, the mysterious woman with the haunting half-smile had vanished. French detectives searched for the painting for more than two years, mistakenly hauling in poet Guillaume Apollinaire and artist Pablo Picasso in hopes of cracking the high-profile case. Then, in December 1913, an Italian house painter contacted a prominent art dealer in Florence, claiming to be in possession of the celebrated portrait. Police swooped in and arrested Vincenzo Peruggia, a former Louvre employee. It turned out Peruggia had walked unnoticed into the museum, removed the “Mona Lisa” from its frame and spirited it out under his clothes. Hailed as a patriot in his native Italy, the burglar served six months in jail for the crime."
Mona Lisa is maybe the most famous painting in the world but I prefer the St. John the Baptist as I told the story here.