John Stuart Mill (20 May 1806 - 8 May 1873) was a British philosopher, political economist and civil servant. He was an influential contributor to social theory, political theory and political economy. He has been called "the most influential English-speaking philosopher of the nineteenth century". Mill's conception of liberty justified the freedom of the individual in opposition to unlimited state control. Mill expresses his view on freedom by illustrating how an individual's drive to better their station, and for self-improvement, is the sole source of true freedom. Only when an individual is able to attain such improvements, without impeding others in their own efforts to do the same, can true freedom prevail. Mill's linking of freedom and self-improvement has inspired many. By establishing that individual efforts to excel have worth, Mill was able to show how they should achieve self-improvement without harming others, or society at large. He was a proponent of utilitarianism, an ethical theory developed by Jeremy Bentham. He worked on the theory of the scientific method. Mill was also a Member of Parliament and an important figure in liberal political philosophy.