Dunno if famed French psychoanalyst and fellow author of impenetrable prose Jacques Lacan (born a generation earlier than Derrida) also suffered from imposter syndrome. But Lacan actually was a fraud for real.

Long hailed as a genius by many in intellectual circles, Lacan stole the basic ideas that he became most famous for - "mirror theory" - from his own teacher, a mentally-ill man who posited that in order to have a sense of self human beings must be able to see our images in modern-day looking glasses. But as it so happened, Lacan's teacher had a condition that caused him to go blind. When he'd lost nearly all his eyesight, he sat himself in front of a glass mirror and blew his brains out - and Lacan then stole his ideas and presented "mirror theory" to the world as his own.