John Charles Turner (7 September 1947 – 24 July 2011) was a British social psychologist who, along with colleagues, developed the self-categorization theory. Amongst other things, the theory states that the self is not a foundational aspect of cognition, but rather that the self is an outcome of cognitive processes and an interaction between the person and the social context. The self-categorization theory was developed as a companion theory to the social identity theory, and the two theories taken together are known as the social identity approach.