James Montgomery Flagg (1877-1960), best known for his "I Want You for U.S. Army" poster, was skilled in oils, watercolors, pen-and-ink, and charcoal.
He was as famous for portraits as for his illustrations, and he did both straight portraits and caricatures.
Here are a few of his caricature portraits of the movie stars. They prove the notion that the key to a likeness is not the physiognomy, but rather the attitude.
James Montgomery Flagg on Wikipedia