Ray Theiss is a Texas historian, researcher, and writer from Llano,Texas. He currently works as a Nuclear Security Officer and previously served as a historical archivist. His academic focus at Angelo State University centered on Texas history and regional studies.

Theiss has been actively involved in historical preservation and public history through organizations such as Fort Concho Living History, the Concho Valley Archaeological Society, Camp Mabry Living History, the Admiral Chester Nimitz Museum of the Pacific War Living History program, and the Southwestern Historical Society. He is currently a member of the Texas Folklore Society.

A frequent public speaker, Theiss has presented for the Fort Concho Speaker Series, the West Texas Historical Association, the Tom Green County Historical Society, the Federation of Southwestern Archaeological Societies, and the Munson Family/Stephen F. Austin State Park Speaker Series. His published work includes contributions to the San Angelo Standard-Times, Lost Treasure Magazine, the Bay City Sentinel, and the anthology Road Kill: Texas Horror Anthology, Vol. 9.

His research interests include Texas history, archaeology, living history interpretation, and creative fiction.