|Died||April 23, 1917 (aged 66)|
|Education||Milwaukee: (H. Viandan, J. Roese); New York: ASL, NAD (Lemuel E. Wilmarth); Munich: Royal Academy (Alexander Strähuber, Franz Xaver Barth, Ludwig von Löfftz, Franz von Defregger) |
Koehler was born in Hamburg; his family spelled their name Köhler until they moved to Milwaukee, Wisconsin in 1854. There he attended the historic German-English Academy. He graduated from the academy in 1865, but continued his lessons with the school's drawing master, Henry Vianden, who had graduated from Munich's Royal Academy of Fine Arts. He apprenticed himself to a lithography firm.
In 1871, he went to New York City for eye surgery, and stayed to work as a lithographer. After studying drawing in the night classes of the National Academy of Design, Koehler went to Munich to study fine art at the Royal Academy in 1873, studying with Karl von Piloty and Ludwig Thiersch. He returned to New York after two years because of depleted funds. In 1879, he was able to return to Munich with means furnished by George Ehret, of New York, whose attention had been drawn to the young artists's ambition and capabilities. On his second trip, he studied under Ludwig Löfftz and Franz Defregger. His friendships with William Merritt Chase and Frank Duveneck date from this time.
Koehler's work while in Munich won him silver and bronze awards from the Academy, and Bavaria's Cross of the Order of St. Michael. Koehler then set himself up as head of a private art school; pupils included Alfons Mucha.
He began to exhibit in the National Academy, New York, in 1877. In 1885 he took charge of a private school of art in that city. He organized the American department of the international art exhibition at Munich in 1883, and was appointed by the Bavarian authorities to act in the same capacity in the exhibition of 1888.
In 1892 Robert Koehler returned to New York City to work as a portrait artist. The following year he moved to Minneapolis, Minnesota, accepting an offer to be the director of the Minneapolis School of Fine Arts (now the Minneapolis College of Art and Design). Koehler was also involved with the establishment of Minneapolis' Museum of Fine Art, now the Minneapolis Institute of Arts. He was a pioneer of art instruction and appreciation in the region.
Koehler was president of the Minnesota State Art Commission from 1903 to 1910, member of the Artists' League of Minneapolis, honorary member of the Minnesota State Art Society, honorary member of the Alumni Association of the Minneapolis School of Art, member of the Society of Western Artists, and member of the Institute des Beaux Arts et des Lettres of Paris, France. He received bronze and silver medals at the Munich Academy, honorable mention at the Paris World's Fair, 1889, bronze medal at the International Art Exhibition at Buenos Aires in 1910, and the cross of the Order of Saint Michael of Bavaria in 1888. Three notable paintings, "The Carpenter's Family," "At the Cafe," and his masterpiece "The Strike" were selected for display at the Columbian Exposition in Chicago in 1893.
Koehler continued working in Minneapolis, painting portraits and landscapes, teaching painting, and arranging exhibitions. He retired as director in 1914. He died in Minneapolis at age 66.
- Holy-day Occupation (1881, at the Pennsylvania Academy of the Fine Arts)
- Her Only Support (1882)
- The Socialist (1883, at the Deutsches Historisches Museum in Berlin)
- The Strike (1886, at the Deutsches Historisches Museum in Berlin) 
- At the Cafe (c. 1887, private collection) 
- Portrait of Alvina Roosen (c. 1900)
- Rainy Evening on Hennepin Avenue (c. 1902)
- Herbjørn Gausta (1915)
- Study Head (Minneapolis Institute of Arts)
- Violet (Minneapolis Athletic Club)
- Portrait of Dean Wulling (State University of Minnesota)
- The Carpenter's Family (collection of Mr. and Mrs. Daniel Elliot, Woodland Hills, CA) 
- The Family Bible
- Salve Luna
- a portrait at the Alexandria, Minnesota public library
- portrait of Etta Chadbourn Ross at the Etta C. Ross Memorial Library Museum at Blue Earth, Minnesota
- National Museum of American Art (U.S.); National Portrait Gallery (Smithsonian Institution) (1993). Revisiting the white city: American art at the 1893 World's Fair. Washington, D.C. : Hanover: National Museum of American Art and National Portrait Gallery, Smithsonian Institution; Distributed by the University Press of New England. p. 275. ISBN 0937311014.
- Rines, George Edwin, ed. (1920). "Koehler, Robert". Encyclopedia Americana.
- Levy, Florence Nightingale (1917). American Art Directory, Volume 14. The American Federation of the Arts. p. 324.
- National Museum of American Art (US) (1993) Revisiting the White City, p. 180
- National Museum of American Art (US) (1993) Revisiting the White City, p. 181
- National Museum of American Art (US) (1993) Revisiting the White City, p. 276
- "The Etta Chadbourn Ross Memorial Library" (PDF). The Pied Cow: The Chadbourne Family Association Newsletter. Fall–Winter 1992. p. 5. Retrieved 17 August 2018.
- Wilson, J. G.; Fiske, J., eds. (1892). "Koehler, Robert". Appletons' Cyclopædia of American Biography. New York: D. Appleton.
- Harold L. Van Doren (1961). "Koehler, Robert". Dictionary of American Biography. V, Part 2. New York: Charles Scribner's Sons. pp. 484–485.
- Colles Baxter Larkin (1999). "Koehler, Robert". American National Biography. 12. New York: Oxford University Press. pp. 857–858.
- Dennis, James M. (2011). Robert Koehler's The Strike: The Improbable Story of an Iconic 1886 Painting of Labor Protest. Madison: University of Wisconsin Press. ISBN 978-0-299-25133-8.