Utilitarianism is a moral theory that advocates for actions that maximize happiness for the greatest number of people, founded by Jeremy Bentham in 1789 and later modified by John Stuart Mill. It is part of consequentialism and includes variations like rule, negative, and preference utilitarianism. Critics argue against quantifying utility, issues of justice, and the demanding nature of the theory, with literary references indicating its social critiques, such as Charles Dickens' 'Hard Times.'