John Stuart Mill was an English philosopher, politician and economist most famous for his contributions to the theory of utilitarianism. The author of numerous influential political treatises, Mill s writings on liberty, freedom of speech, democracy and economics have helped to form the foundation of modern liberal thought. His 1859 work, On Liberty, is particularly noteworthy for helping to address the nature and limits of the power of the state over the individual. Mills has become one of the most influential figures in nineteenth-century philosophy, and his writings are still widely studied and analyzed by scholars. Mills died in 1873 at the age of 66.