Robert Jenkins Onderdonk (January 16, 1852 - July 2, 1917) was an American artist and art teacher from San Antonio and Dallas. Born in Catonsville, Maryland, he was an important artist in early Texas art and was known as the "Dean of Texas Artists" after he traveled to Texas in 1878.
Two of his three children were important Texas artists; Eleanor (1884-1964) was a respected miniaturist and Julian (1882-1922) was known as the "Bluebonnet painter."
His masterpiece is the 1903 painting Fall of the Alamo which is held at the Texas State Archives. A portion of this painting was used as the cover artwork for the game The Alamo.