Here it is: that famous portrait of Napoleon Bonaparte with his hand in his coat (or his tunic, actually). The title is The Emperor Napoleon in His Study at the Tuileries and it was painted in 1812 by the great Jacques-Louis David.
Yes, this is the painting that inspired centuries of imitations and quips about why Napoleon had his hand tucked into his tunic. (According to the National Gallery of Art, "David may have represented Napoleon with his hand in this position because, before pants had pockets, men sometimes stood this way to show that they were calm, comfortable, and relaxed.") The painting is now part of the Samuel H. Kress Collection at the National Gallery of Art.