He is the subject of a [link|http://www.amazon.com/exec/obidos/ASIN/0743224574/nobelprizeintern/104-1062501-0633546|book] and a movie "A Beautiful Mind", and which of course you have not seen. He is a paranoid schizophrenic.

See his autobiographical sketch after he won the [link|http://www.nobel.se/economics/laureates/1994/nash-autobio.html|Nobel] prize in 1994 for his contributions to Economic Sciences - for pioneering analysis of equilibria in the theory of non-cooperative games.

Here is a [link|http://pup.princeton.edu/titles/7238.html|Princeton University link]:

From 1959 until his astonishing remission three decades later, the man behind the concepts "Nash equilibrium" and "Nash bargaining"--concepts that today pervade not only economics but nuclear strategy and contract talks in major league sports--had lived in the shadow of a condition diagnosed as paranoid schizophrenia. In the introduction to this book, Nasar recounts how Nash had, by the age of thirty, gone from being a wunderkind at Princeton and a rising mathematical star at MIT to the depths of mental illness.