Alan Kay
Alan Kay is best known for his early work on object-oriented programming using the Smalltalk language which resulted in his Dynabook concept. His concept has never been fully implemented although a modern tablet PC running Squeak comes close. He is one of the core team that produced Squeak and he has also created another Smalltalk based project in 3 dimensions, Croquet. He has also done work in constructionist education.
This book chapter on Personal Dynamic Media shows what Alan was working on in 1977.
And in this essay he describes what the Etoys activity is all about OLPCEtoys.pdf
In 1987, while at Apple, he created a video called Knowledge Navigator to demonstrate his vision of fully interactive computing.
More info here: http://en.wikipedia.org/wiki/Alan_Kay
Partial transcription of Alan Kay's talk on the 40th Anniversary of the Dynabook Idea at the Computer History Museum: "after 40 years the dynabook is not here yet".