It was a [link|http://www.smalltalk.org/|team effort at Xerox PARC]. Quoting a Dr. Dobb's article:
"The recipients of this year's award, Adele Goldberg and Dan Ingalls, are pioneers in the area of object-oriented programming in general, and the Smalltalk language and development environment in particular. As researchers at Xerox's Palo Alto Research Center (PARC), Goldberg and Ingalls each recognized in their own way the promise of objects, and they were in a unique position to put those theories into practice in an architecture based on objects at every level."