wikipedia entry: http://en.wikipedia.org/wiki/John_McCarthy_(computer_scientist)
important contributions (as per I know)
* initiated the 'Time-Sharing' mechanism
* did initial development in field of A.I.
* creator of programming language 'Lisp' (just younger to Fortran)
* coined the term 'Artificial Intelligence'
* Invented Automatic Garbage Collection.
* published several Mathematical and Computational Logic Papers; even one of the initial papers on E-Commerce referred to as 'buying and selling by computers'
* even tried promoting his ideas through medium of literature, a science fiction made public by him..... 'The Robot and The Baby' (download as PDF).
Links to know more:
* First contribution mentioned wasn't known to me until I came across Herb Sutter's following article http://herbsutter.com/2011/10/25/john-mccarthy/
* "History of Lisp" by John McCarthy http://www-formal.stanford.edu/jmc/history/lisp/lisp.html
* a Youtube Video: http://www.youtube.com/watch?v=kvIqc0aBR0A