Karl Joseph Leyser TD FBA (24 October 1920 – 27 May 1992) was a German-born British historian who was Fellow and Tutor in History, Magdalen College, Oxford, from 1948 to 1984, and Chichele Professor of Medieval History at Oxford University, from 1984 to 1988.
Because he was Jewish, he escaped the Nazis before World War II and served with the British Army. He was married to Henrietta Leyser, and his daughter is the scientist Ottoline Leyser.