Alan Kay Did Not Invent Objects

The famous 1981 Byte magazine issue that popularized Smalltalk and OOP explicitly says “the fundamental idea of objects, messages, and classes came from SIMULA.” More recently people keep claiming that OOP “isn’t really” about classes and objects and the important bit is actually the messages. In the Smalltalk-72 manual he says (p. 18)

Looking at the early sources, everybody acts as if OOP consisted of three major ideas: classes that defined protocol and implementation, objects as instances of classes, and messages as the means of communication.

Source: www.hillelwayne.com