Along with Bill Gosper, he may be considered to have founded the hacker community,[1] and holds a place of distinction in the communities of the programming language Lisp and of the Massachusetts Institute of Technology (MIT) Artificial Intelligence Laboratory.

At that time, Peter Samson had written a program in Fortran for the IBM 709 series machines, to automate the tedious business of writing the intricate timetables for the Railroad Club's vast model train layout.

Years later, elements of this compiler (combined with some ideas from fellow TMRC member Steven Piner, the author of a very early PDP-4 Fortran compiler while working for Digital Equipment Corporation) were typed in and "showed signs of life".

This and other experiences at TMRC, especially the influence of Alan Kotok, who worked at DEC and was the junior partner of the design team for the PDP-6 computer, led Greenblatt to the AI Lab, where he proceeded to become a "hacker's hacker" noted for his programming acumen as described in Steven Levy's Hackers: Heroes of the Computer Revolution, and as acknowledged by Gerald Jay Sussman and Harold Abelson when they said they were fortunate to have been apprentice programmers at the feet of Bill Gosper and Richard Greenblatt.

[3] Indeed, he spent so much time programming the Programmed Data Processor (PDP) machines there that he failed out of MIT as a first-term junior and had to take a job at a firm, Charles Adams Associates, until the AI Lab hired him about 6 months later.