The Mona Lisa Was Considered Unremarkable for Centuries

For most of its existence, the Mona Lisa was considered a competent but unremarkable work — it hung in Napoleon's bedroom before being moved to the Louvre. It became the world's most famous painting largely because it was stolen in 1911 by Vincenzo Peruggia, an Italian nationalist who wanted to return it to Italy. The two-year theft and recovery made it a global sensation.

Source: The Crimes of Paris — Dorothy and Thomas Hoobler