Alan Kay invented Smalltalk. In so doing, he can be said to have invented object oriented programming, although there are important precursors to Smalltalk in that regard.
Simula, a language form the 1960s for writing simulations was one. another was Planner, a language invented by Carl Hewitt of MIT. Alan Kay specifically gives credit to Hewitt for influencing him while he was at Xerox PARC.
