Discourse theory has always played a significant role in Michel Foucault's larger theoretical framework. His discourse theories integrate language, power, and knowledge as to achieve the 'truth,' though there is a debate whether they are inherently linked. This paper explores the longitudinal evolution of Foucault's discourse theory from the external and internal aspects. It examined the evolution of Foucault's discourse theory through different stages, closely focusing on the efforts that he gradually made to perfect his discourse theory. Adopting a qualitative research design, the study established how language, power, and knowledge constituted three fulcrums of Foucault's discourse theory as it evolved. The findings indicate that Foucault introduced a novel concept into discourse theory when he established the internal relationship between language, power and knowledge and with insanity and sexuality as external aspects. His theories of madness (insanity) and sexuality did not so intellectually trigger the masses, but he succeeded in linking insanity and sexuality with language, power and knowledge, which are the center of Foucault's discourse theory. This evolution of the discourse theory is the evidence of the transformation and development of discourse production, power production, and knowledge production, which helped Foucault to establish his discourse theory. The study implies that knowledge is the link between Foucault's discourse analysis and power analysis and that Foucault's discourse theory is the representation of his core discourse thoughts placed among discourse, knowledge, and power.