Piero della Francesca's Hercules, a fresco in the Isabella Stewart Gardner Museum in Boston, and the painter's only secular work, is unique among his paintings in many respects. Although its authenticity as an autograph work has never been questioned, it is usually neglected in the literature on Piero. The fresco comes from the painter's own house in Borgo San Sepolcro and thus is an exceptional case of an artist's self-patronage. The analogy of composition and dimensions with Piero's later portrait, as well as iconographic attributes of the virtue of Prudence and some other clues, lead the author to make a convincing notion that the Hercules is Piero's self-portrait, what is more, a "moral" one, characterising him as an artist.