Judith Butler (b. February 24, 1956) is an American feminist, post-structuralist philosopher. She has the post of Professor of Comparative Literature and Rhetoric at the University of California, Berkeley. Butler has worked heavily in the area of gender and queer studies, challenging in Gender Trouble the idea of a binary gender duality, pointing out that gender roles, sexual preference, sexual identity and related properties are a matter of performance - a person is not a man or a woman, but plays that role as part of a larger sexual identity. This idea is 'non-essentialist', in that Butler rejects the idea that there is any particular essential characteristic to identity, instead thinking that one's social identity is chosen.
These insights have been used as part of a critical stance to perform analysis on works of art and literature that deal with the topic of sexuality and gender. For instance, such an analysis could be used to understand the pop star Madonna whose sexual identity seems to fluctuate and who makes great commercial success out of messing with the notion of gender identity as fixed.