Robert George Siebecker (October 17, 1854 – February 12, 1922) was an American attorney and the 11th Chief Justice of the Wisconsin Supreme Court. He served on the Wisconsin Supreme Court for the last 19 years of his life (1903–1922). Before being appointed to the Supreme Court, he served 13 years as a Wisconsin circuit court judge in central Wisconsin (Dane, Sauk, Columbia, and Marquette counties) and was a law partner of Robert M. "Fighting Bob" La Follette.