He was trained as a fine artist but achieved fame as an illustrator of books and magazines.
His father, an amateur artist, encouraged Robert's interest in art.
He attended the Slade School of Art in London, then returned to the United States to pursue a career in fine arts, although he had to work as a commercial artist to support himself.
He produced story illustrations and full-page ads that appeared in The Saturday Evening Post, Collier's, Holiday, and Cosmopolitan bringing a superb sense of composition to his advertisement work.
His work for Collier's magazine included detailed illustrations accompanying a series of Sherlock Holmes stories.