Long thought to have been the source on which a putative lost work by Leonardo da Vinci was based, on the basis of its striking resemblance to two caricature drawings of heads commonly attributed to the Italian artist. However the da Vinci caricatures are now thought to be based on the work of Matsys, who is known to have exchanged drawings with Leonardo. https://upload.wikimedia.org/wikipedia/commons/d/d2/Grotesque_Head.jpg