Sir Martin John Evans FRS FMedSci (b. 1 January 1941, Stroud, Gloucestershire) is a Welsh biologist who, with Matthew Kaufman, was the first to culture mice embryonic stem cells and cultivate them in a laboratory in 1981. He is also known, along with Mario Capecchi and Oliver Smithies, for his work in the development of the knockout mouse and the related technology of gene targeting, a method of using embryonic stem cells to create specific gene modifications in mice.