Sir Peter Brian Medawar (28 February 1915 – 2 October 1987) was a Brazilian/British biologist, whose work on graft rejection and the discovery of acquired immune tolerance was fundamental to the practice of tissue and organ transplants. He was awarded the 1960 Nobel Prize in Physiology or Medicine with Sir Frank Macfarlane Burnet.
Until he was partially disabled by a cerebral infarction, Medawar was Director of the National Institute for Medical Research at Mill Hill.
Medawar was born on 28 February 1915, in Petrópolis, Brazil (a town 40 miles north of Rio de Janeiro) of a British mother (née Edith Muriel Dowling) and a Lebanese father, Nicholas Medawar, who was a Maronite Catholic. Medawar left Brazil for England in 1928, and lived there for the rest of his life.
Medawar was educated at Marlborough College and Magdalen College, Oxford, where he eventually became a Fellow.