"William E. Emba"
The title character, called Mailman, is a mentally ill mailman
with criminal and deviant behavior with respect to the mail that
he handles. It turns out that Mailman had once been a mathematics
graduate student, "working out a routine problem in fluid dynamics",
but he went off on tangents until he worked out mathematical theories
of everything, including intelligence, economics, art, love and war.
His supervisors failed to understand the resulting equations and
diagrams. This was followed by a nervous breakdown. After Mailman
recovered, he quit school and joined the postal service.
This short story was rewritten and expanded to a novel (2003)
of the same title, with the title character becoming a former
physics undergraduate student who had lost it all with his
theory of everything.