Robert Ammann (from Wikipedia):

Robert Ammann [...] was an amateur mathematician who made several significant and groundbreaking contributions to the theory of quasicrystals and aperiodic tilings.

Ammann attended Brandeis University, but generally did not go to classes, and left after three years. He worked as a programmer for Honeywell. After ten years, his position was eliminated as part of a routine cutback, and Ammann ended up working as a mail sorter for a post office.

He discovered several new aperiodic tilings, each among the simplest known examples of aperiodic sets of tiles. He also showed how to generate tilings using lines in the plane as guides for lines marked on the tiles, now called "Ammann bars".

Ammann's discoveries came to notice only after Penrose had published his own discovery and gained priority.

He published one paper with Grünbaum and Shephard.

mathpapers/results by amateurs.... $\endgroup$ – Barry Cipra May 31 '13 at 13:13