Michel Foucault

M.F.: /---/ I think that central issue of philosophy and critical thought since the eighteenth century has always been, still is, and will, I hope, remain the question: What is this Reason that we use? What are its historical effects? What are the limits, and what are its dangers? How can we exist as rational beings, fortunately committed to practicing a rationality that is unfortunately crisscrossed by intrinsic dangers? One should remain as close to this question as possible, keeping in mind that it is both central and extremely difficult to resolve. /---/
1984 “Space, Knowledge, and Power” in P.Rabinow (ed.) 1984 The Foucault Reader.

Wikipedia:
Michel Foucault (French pronunciation: [miʃɛl fuko]), born Paul-Michel Foucault (15 October 1926 – 25 June 1984), was a French philosopher, sociologist, and historian of ideas. He held a chair at the prestigious Collège de France with the title "History of Systems of Thought," and also taught at the University at Buffalo and the University of California, Berkeley.
Foucault is best known for his critical studies of social institutions, most notably psychiatry, medicine, the human sciences, and the prison system, as well as for his work on the history of human sexuality. His writings on power, knowledge, and discourse have been widely influential. In the 1960s Foucault was associated with structuralism, a movement from which he distanced himself. Foucault also rejected the poststructuralist and postmodernist labels later attributed to him, preferring to classify his thought as a critical history of modernity rooted in Kant. Foucault's project was particularly influenced by Nietzsche, his "genealogy of knowledge" a direct allusion to Nietzsche's "genealogy of morality". In a late interview he definitively stated: "I am a Nietzschean."
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Foucault's personal life during the École Normale was difficult—he suffered from acute depression. As a result, he was taken to see a psychiatrist. During this time, Foucault became fascinated with psychology.

Wikipedia:
Acute depression.
Major depressive disorder (MDD) (also known as recurrent depressive disorder, clinical depression, major depression, unipolar depression, or unipolar disorder) is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities.