Who was Jacques Derrida, and why does he have such a towering, and foreboding reputation across modern philosophy? For some he is the source of the crisis of alternative facts. For far-right terrorist Anders Brievik, ‘Derridian deconstruction’ was the cause for the end of truth. In 1992, 18 philosophers wrote an open letter to complain when he was awarded an honorary degree by Cambridge University. For others, he is a film star thinker who covered every possible subject from literature, politics, and language. Here Peter Salmon introduces the key concepts, showing that, despite the impression of being eclectic, Derrida was a writer who spent his life on a series of interlinked themes: ethics, friendship and language.