The Mona Lisa wasn’t always an icon. Before 1911 Leonardo’s painting was certainly known and respected, but it wasn’t yet the most famous, most adored, most duplicated, and most parodied piece of art in the world. It was not yet the symbol and pop culture juggernaut that it is today. What made the Mona Lisa famous its theft at the hands of Vincenzo Peruggia who, along with two accomplices, lifted the painting off of the wall of the Louvre and simply walked out with it. He kept the portrait in a box in his apartment for over two years before attempting to ransom it, and, upon its return, the Mona Lisa went from merely a respected piece of Renaissance art to the single most famous painting in the world.
The image below shows the blank spot left by Peruggia, and the four wall hooks that had previously held the Mona Lisa before its 1911 abduction.