The British physicist Paul Adrien Maurice Dirac (1902-1984) studied engineering as an undergraduate at Bristol University, but switched to mathematics after graduating. He was one of the pioneers of quantum mechanics, and developed the first theory of the electron that took into account special relativity. The theory worked amazingly well, describing many observed attributes of the electron that previous theories had been unable to anticipate. But the most remarkable prediction of the theory was that the electron should have an anti-particle associated with it, having the same mass, but with a positive instead of negative charge. In 1932 this particleólater called the positronówas discovered, and since then many other anti-particles have been predicted and observed. From 1932 to 1969, Dirac was Lucasian Professor of Mathematics at Cambridge, a post once held by Isaac Newton and currently by Stephen Hawking.