Sir Peter Brian Medawar (; 28 February 1915 – 2 October 1987) was a British biologist born in Brazil, whose work on graft rejection and the discovery of acquired immune tolerance was fundamental to the practice of tissue and organ transplants. For his works in immunology he is regarded as the "father of transplantation". He is remembered for his wit in real life and popular writings. Famous zoologists such as Richard Dawkins referred to him as "the wittiest of all scientific writers", and Stephen Jay Gould as "the cleverest man I have ever known".Medawar was the younger son of a Lebanese father and a British mother, and was a naturalised British citizen. He studied at Marlborough College and Magdalen College, Oxford and was professor of zoology at the University of Birmingham and University College London. Until he was partially disabled by a cerebral infarction, he was Director of the National Institute for Medical Research at Mill Hill. With his doctoral student Leslie Brent and postdoctoral fellow Rupert E. Billingham, he demonstrated the principle of acquired immunological tolerance (the phenomenon of unresponsiveness of the immune system to certain molecules), which was theoretically predicted by Sir Frank Macfarlane Burnet. This became the foundation of tissue and organ transplantation. He and Burnet shared the 1960 Nobel Prize in Physiology or Medicine "for discovery of acquired immunological tolerance".