The prominent libertine philosopher known for his work in political philosophy is John Stuart Mill. He was a 19th-century British thinker who advocated for individual liberty, utilitarianism, and personal freedom. Mill believed in the importance of self-expression and the protection of individual rights against societal constraints. His influential works, including "On Liberty," highlighted the need for freedom of thought and expression as essential components of a progressive society. Mill's ideas on personal autonomy and the role of government in regulating behavior continue to resonate in contemporary debates on civil liberties and social justice.