Denslow was a humor and political cartoonist for a magazine called Philistine.  He was born in Philadelphia but by 1890 was living in Chicago, where he met L. Frank Baum.  Baum was impressed enough by Denslow's work that Denslow eventually provided illustrations for several of Baum's books, among them The Wonderful Wizard of Oz.

He and Baum had a falling out over royalties from the 1902 stage version of The Wizard of Oz, for which Denslow designed the sets and costumes.  Nevertheless, Denslow became quite wealthy from royalties from the books and the play.  He purchased himself a small island off the coast of Bermuda where he lived out the rest of his days, dying in obscurity due to pneumonia and probably the effects of alcoholism.

He had a characteristic signature which included a stylized representation of a seahorse, as show in the autographed photo above.

Denslow was said to have preferred the corncob pipe because it was so light that it rarely required a hand to hold it, which kept both hands free for his work.