Paul Dirac is one of the most prominent physicists of the 20th century who established the most general theory of quantum mechanics in Hilbert space and discovered the relativistic equation for the electron, which now bears his name. Dirac's bra-ket notation using angle brackets and a vertical bar is iconic for quantum physics and is widely used to write quantum mechanical equations in their most general, basis-independent form. For his remarkable achievements, including the discovery of an antiparticle to each fermion particle, Dirac received the 1933 Nobel Prize for physics.