Edouard Manet, The Execution of Emperor Maximilian, 1869. Oil on canvas, 99" x 119."
Pulling off a political painting (or political art generally) is a tricky business; it can become preachy or corny or strident so easily. This is one of the best examples I can think of, and it was great to finally see it in person at MOMA last year.
Someday I'm going to have posters like this made for exhibitions of my work (and charge two bits to get in):