Paul Dirac, in 1928, is going to extend the work of Pauli, his so called Pauli equation. The Pauli equation, describes the spin of electrons. Dirac extended the equation, indeed, to account for special relativity. Thus, the Dirac wave equation, was a "relativistic wave equation." The equation is consistent, both with quantum mechanics and special relativity. The Dirac equation could also describe all massive spin-1/2 particles, such as quarks and the electron. The idea was that the equation could describe electrons that orbit the atomic nucleus at significant fractions of the speed of light.
Another interesting result emerged from this work by Dirac. When the results would yield negative for the value of energy of the electron, Dirac thought fast. He proposed a solution, the existence of an antimatter counterpart to the electron: the positron. Every elementary particle has a corresponding antiparticle. Antiparticles have the same mass as their normal particle counterpart, however, opposite electric charge. When a particle and it's antiparticle meet, they are both destroyed in a burst of energy known as annihilation. Indeed, the relativistic Dirac wave equation, predicted the existence of antimatter. Antimatter was experimentally confirmed to exist in 1932 by Carl D. Anderson.
Paul Dirac, in 1928, proposed a relativistic wave equation, known as the Dirac equation, to describe electron orbits at significant fractions of the speed of light. In so doing, Dirac predicted the existence of antimatter.