Paul Dirac, a British mathematician, also developed a quantum theory in 1925, which were also based upon Hamilton's classical mechanics ideas. It was ultimately transformed into a very versatile system of quantum mechanics, but it was not as immediately obvious as was Schrödinger's wave mechanics. So it suffered a similar fate to Heisenberg's Matrix Mechanics. Nevertheless, Dirac's real claim to fame came in 1928 when he did accomplish what eluded Schrödinger from the outset - that is a quantum theory which was Lorentz-invariant and obeyed the requirements of Einstein's Special Theory of Relativity. Relativistic Quantum Mechanics provided explanations for the concept of spin and predicted the existence of positrons.