George Sinclair (Sinclar) (ca.1630–1696) was a Scottish mathematician, engineer and demonologist. The first Professor of Mathematics at the University of Glasgow, he is known for Satan's Invisible World Discovered, (c. 1685), a work on witchcraft. He wrote in all three areas of his interests, including an account of the "Glenluce Devil", a poltergeist case from c. 1654, in a 1672 book mainly on hydrostatics but also a pioneering study of geological structures through his experience in coal mines.