Check out Common Lisp, which was the first standardized OOP language (1994) with its Common Lisp Object System. Classes, class hierarchies, meta-classes, ... al

Check out Common Lisp, which was the first standardized OOP language (1994) with its Common Lisp Object System. Classes, class hierarchies, meta-classes, ... all there. It's not using message passing, but that can be viewed as a simple case of its generic functions...