I know post colonial studies which is a critical theory began with Orientalism which uses Foucault's concept of discourse. But also Frankfurt School is widely credited with finding critical theory since they wanted to reform marxism and change it from its singular focus on class to showing how western society in general perpetuated power hierarchies aka critical theory ? Whereas postmodernists use genealogies to show that all "Truths" are usually only dominant because of their contribution to re-affirming power. For eg. the universality of representative bourgeois democracy helps perpetuate patriarchy and majority rule.