James Montgomery Flagg (1877-1960) was one of America's most popular illustrators from early in the twentieth century through the 1930s, and to a lesser extent beyond, as his sketchy style fell out of synch with illustration fashion.

A brief Wikipedia biography is here, but more useful sources are here (for details) and here, where you can scroll to view examples of his work.

I am ambivalent regarding Flagg's art. That might be because it's a little too loose and too stylized for me. Let me elaborate. The looseness could drift towards a lack of control. As for stylization, his faces sometimes came off more Flagg-like than how peoples actually appeared. I'll point out examples below. On the other hand, he was quite capable of "nailing it," and I'll point that out too.

Gallery

[Image]Army recruiting poster - 1917
This is by far Flagg's most famous work: iconic to this day.

[Image]Illustration for Judge magazine cover, 31 March 1917
Flagg could paint in oils, but that was done mostly when he wasn't illustrating.

[Image]Pen and ink illustration
Much of Flagg's illustration work was for magazine interiors, rather than covers. Before the 1920s, he often used pen-and-ink, as did many other illustrators at that time. (This illustration seems to be from the 30s, however, so he continued to use a pen when he could get away with it.)

[Image]Wash or watercolor illustration - 1930s
By the 1920s and 30s, he had largely switched to water media. The girl is nicely done, but the Rolls-Royce in the background is far too sketchily done (inaccurately drawn) to suit me.

[Image]In Liberty Magazine - 27 October 1934
But here Flagg shines. Not the whole illustration, but with the seated women. Especially the expression on her face.

[Image]Sketch of actress Jean Harlow
This is an example of Flagg-style taking over bits of portraiture. Yes, it looks like Harlow. And yes, there's no mistaking who drew her.

[Image]"Lost Horizon" poster - 1937
More Flagg intrusion, especially his treatment of the subjects' noses and the general sketchiness that detracts from what many people expect from a movie poster. Flagg's treatment of Ronald Colman's right shoulder is just plain wrong.