In "The Quantum Theory of the Electron," Proceedings of the Royal Society. Series A 117 (778) (1928) 610–24 English theoretical physicist Paul Dirac proposed the Dirac equation as a relativistic equation of motion for the wavefunction of the electron. This work led Dirac to predict the existence of the positron, which he interpreted in terms of what came to be called the Dirac sea. The positron was observed by Carl Anderson in 1932. Dirac's equation also contributed to explaining the origin of quantum spin as a relativistic phenomenon.
Even among sometimes eccentric theoretical physicists Dirac's behavior stood out; he was known to exhibit autistic traits that made him appear very unusual. Einstein said of him, "This balancing on the dizzying path between genius and madness is awful."
In 1975, Dirac gave a series of five lectures at the University of New South Wales which were subsequently published as a book, Directions in Physics (1978). Remarkably these lectures, which seem to have been given without notes, were filmed. Nothing in the lectures makes Dirac seem particularly eccentric. In 2013 the films of several of these lectures, which had developed quality problems, were made available on YouTube. They may be the only extensive films of Dirac lecturing.