Robert Jenkins Onderdonk (January 16, 1852 – July 2, 1917) was an American painter and art teacher, born in Catonsville, Maryland.
An important artist in the first stage of Texas art, he was a long-time art teacher in San Antonio and Dallas, where he formed art associations and leagues; for his contributions to the culture of art and painting in Texas he is known as the "Dean of Texas's Artists."