Immediately after SIMULA I was finished, the designers decided to work on a new language which would contain many more features so that it could be used for more general purpose areas. The result was SIMLUA 67. To help make simulation easier, SIMULA 67 introduced the concept of classes,including instancing and coroutine. This was the beginning of data abstraction.
Source: "Concepts of Programming Languages" by Robert W. Sebesta, The Benjamin/Cummings Publishing Company, Inc, 1993