Robert Nozick was a 20^th-century American political philosopher. He's best known for writing the book Anarchy, State, and Utopia, which defended free-market libertarianism. In addition to his political theories, he also contributed ideas to the fields of epistemology (the theory of knowledge) and the metaphysics of personal identity. Read more about his work here.

Nozick designed his Experience Machine thought experiment to refute the beliefs of hedonists. Hedonism is a form of utilitarianism, a philosophy that that says that the greatest moral action is one that maximizes "utility." Utility has been defined in many different ways, all relating to a feeling, perceiving entity's general well-being, but a number of 18^th- and 19^th-century utilitarian philosophers like Jeremy Bentham and John Stuart Mill took "hedonistic" views of the concept, equating "utility" with "pleasure." Sound interesting? Read more about hedonism and the many other forms of utilitarianism here.