One of the first attempts at a relativistic quantum mechanical wave equation was the Klein-Gordon (KG) equation. Though it is theoretically sound from the perspective that it is consistent with both classical quantum mechanics and the special theory of relativity, it has several unsavory features which keep it from being a very powerful tool in relativistic quantum mechanics. Dirac later developed his own relativistic wave equation which did not have some of the shortcomings of the Klein-Gordon equation. Dirac's formulation also led to the discovery that some of the supposed ``errors'' of the KG equation were actually illustrating some new physics. The Dirac equation is only rigorous for a one particle system, but has been used as a starting point for a number of approximate many electron methods.