John Stuart Mill “On Liberty” John Stuart Mill (1806–1873) was a British philosopher, sociologist, economist, and politician. He made a significant contribution to the development of social science, political science, and political economy. There is an opinion that Mill was the most prominent English-language philosopher of the 19th century. He was called “the most influential English-language philosopher of the nineteenth century.” Mill’s concept of liberty justified individual freedom against unlimited state and social control.