Answer: Gilbert Ryle
The phrase "ghost in the machine" was used by Gilbert Ryle in his 1949 book The Concept of Mind to describe the dualism of Descartes. According to Descartes, the human body may be a machine, but it only became a "person" when it was infused with an immaterial soul. The two thus produce a dualistic system of substances, one material and the other immaterial, neither or which could be reduced to the other. Ryle rejected and criticized this view in his work.For more on Ryle, see the extensive entry about him at the Stanford Encylopedia of Philosophy.