Piero della Francesca's Hercules (ca. 1470)

This painting holds infinite appeal for me. Sometimes you come across a work that changes your worldview and makes you reconsider something you thought you knew. This painting is like the Madeline L'Engle book A Wrinkle In Time in that regard for me. You thought you knew what time was and what space was, but she made you think again. The work expands your concept of the possible.

Piero's Hercules is not the Hercules I thought I knew. He's less physically imposing and more vulnerable than I had ever imagines, and it makes me identify with the man in ways I never could before. He's less professional wrestler and more Olympic athlete. He's doing his best, but sometimes his best is exactly the wrong thing. Thus the insecure knock-knees, and the plaintive gaze. This Hercules makes sense to me; I can see the man in this painting beating his wife and children to death and coming out of his god-induced insanity with the determination to serve an impossible penance that turns his accursed physical prowes to his advantage. This Hercules is doomed to be more beast than man.

And I like how the lion's paws both modestly cover and immodestly imitate Hercules's genitals.

See the painting yourself high on the wall on the second floor of the excellent Isabella Stewart Gardner Museum in Boston (the same room features a great Fra Angelico somewhat hidden on the far side of the fireplace, so look lively, folks).