Louis Michel Eilshemius was an American painter, primarily of landscapes and nudes. Although he was academically trained, much of his work has the unselfconscious character of naive art.

Born into a wealthy family near Newark, New Jersey, Eilshemius was educated in Europe, after which he spent two years at Cornell University before beginning his art studies at the Art Students League of New York. He also studied privately with the American landscape painter Robert Crannell Minor (1839-1904). He subsequently studied under Bouguereau at the Académie Julian in Paris and traveled widely in Europe, Africa and the South Seas, returning to the family brownstone in New York City where he was to live for the rest of his life.

His early landscapes, which show the influence of the Barbizon School and of Corot, George Inness and Albert Pinkham Ryder gained him little recognition from critics or the public. Around 1910, the element of fantasy in his work became more pronounced and his technique became coarser; henceforth, he often painted on cardboard instead of canvas. As his works became more idiosyncratic, so did his behavior, and he developed an unsettling habit of visiting galleries and loudly condemning the works on display.

His later, visionary works depicting moonlit landscapes populated with voluptuous nymphs caused his contemporaries particular consternation, due to their crudely rendered and often extravagantly smiling nudes. These are shown frolicking in forests or waterfalls, either alone or in groups, sometimes defying gravity by floating through the air. His paintings of New York rooftops are as lyrical as his pastoral scenes, and like them are often bounded by sinuous "frames" he painted onto his pictures.

Eilshemius also wrote verse and prose, composed music, painted, philosophized and became notorious for his numerous, often vitriolic, letters-to-the-editor of various New York City publications. His lack of public acclaim led him to desperate measures: suspecting that the length of his name was responsible for his neglect, in about 1890 he began signing his paintings "Elshemus" (he reverted to the original spelling in 1913). On letterheads and in hyperbolic, self-published flyers he would proclaim his accomplishments: "Educator, Ex-actor, Amateur All-around Doctor, Mesmerist-Prophet and Mystic, Reader of Hands and Faces, Linguist of 5 languages", as well as world-class athlete and marksman, "Spirit-Painter Supreme", and musician whose improvisations rivaled the compositions of Chopin. All of this only reinforced the impression, already suggested by the peculiar imagery in many of his paintings, that he was either mad or a charlatan.