Mona Lisa (now also naked!)

''Mona Lisa is "undoubtedly" Lisa Gherardini del Giocondo, according to Veit Probst, director of the Heidelberg University Library.'' [source]

And there is more:
''Leonardo da Vinci, in a Renaissance version of Mad Magazine, may have painted his famous Mona Lisa in a number of ways, including nude.'' [source, and image]