Cornelius Castoriadis[a] (Greek: Κορνήλιος Καστοριάδης;[b] 11 March 1922 – 26 December 1997) was a Greek-French philosopher, social critic, economist, psychoanalyst, author of The Imaginary Institution of Society, and co-founder of the Socialisme ou Barbarie group. His writings on autonomy and social institutions have been influential in both academic and activist circles.