Mat Roy Thompson (February 8, 1874 – June 8, 1962), known also as Matt Roy Thompson, Matthew R. Thompson, Mathew R. Thompson, M. Roy Thompson, Roy Thompson, and Leroy Thompson, was a civil engineer and architect who worked on a great variety of construction and development projects across the United States, most notably on Scotty's Castle, the Death Valley mansion of eccentric millionaire Albert Mussey Johnson.