The wiki article on Dirac quotes Einstein as saying of Dirac
I have trouble with Dirac. This balancing on the dizzying path between genius and madness is awful.
I don't understand Dirac at all.
But did Einstein have anything to say about the Dirac equation itself? I remember reading somewhere that he called the Schrodinger equation "a stroke of genius". So surely he must have at least been glad that Dirac had found the special relativistic version of it. Did he offer any insight on what he thought the 4-component wavefunction or the gamma matrices could mean? (I know they have since been elucidated to some degree by the work of e.g. Hestenes.) Any thoughts about anti-matter, spin being an integral part of the wavefunction, or other consequences?