Lionel Penrosel FRS (1898 – 1972) was a British psychiatrist, medical geneticist, mathematician and chess theorist.
The Penrose triangle, also known as the Penrose tribar, is an impossible object. It was first created by the Swedish artist Oscar Reutersvärd in 1934. With his mathematician son, Roger, Lionel Penrose independently devised and popularised the tribal in the 1950s, describing it as “impossibility in its purest form”. It is featured prominently in the works of artist M. C. Escher, whose earlier depictions of impossible objects partly inspired it.