Philosopher and proponent of utilitarianism John Stuart Mill was born in London England in 1806 and died in 1873. His father James Mill completely took charge of young John's education, subjecting him to a rigid system of intellectual and physical discipline and keeping him away from other boys his age. John Stuart Mill (who I will hereafter refer to as Mill) later said that his education gave him an intellectual advantage over others, but stunted his practical and emotional life and undermined his physical health.
James Mill's pedagogical goals for his son seemed to be aimed at molding him into a perfect utilitarian, one who believed in the greatest happiness of the greatest number, and in this he was quite successful. Jeremy Bentham, John Mill's friend and mentor, was Mill's godfather, and Mill obliged his father's wishes by becoming an avid, indeed fanatical, convert to utilitarianism. He founded a utilitiarian debating society at the tender age of 16 and promoted libertarian and utilitarian ideas throughout his life.
John Stuart Mill was a prolific writer on a wide variety of philosophical, political, economic, and social subjects, and he published innumerable articles, pamphlets, and several books. He first published in the Westminster Review, a journal founded by Bentham and James Mill to propogate libertarian views, or radical ideas as they were known at the time. However, he did not have to rely on writing to make a living, for his father secured him a post with the East India Company.
Mill experienced a profound disillusionment and depression in 1826-7, when he realized that the reforms he worked so hard to foment would not give him satisfaction. He was unhappy, he felt no joy. However, he weathered this storm and eventually found that his capacity for emotion was not completely dulled. Thereafter he began writing again with renewed vigour. Mill wrote in support of the idea of enfranchisement for women, proportional representation, and public ballotting. He became a Member of Parliament as a Radical in 1865, after which he advocated for parliamentary reform and female suffrage; however, his attacks on colonialism in the West Indies made him unpopular, and he was defeated in 1868.
Also in his twenties Mill began a long association with Harriet Taylor, who co-authored pieces with him, though they usually appeared under Mill's name alone. Harriet was married, and her husband was unwilling to grant her a divorce, so she was not free to marry Mill until after her husband's death in 1851.
Perhaps Mill's most important work was his essay On Liberty, a treatise on political liberalism which was a defence of the rights of the individual against the state. He argued cogently that it was only for self protection that anyone, or any state, had any right to interfere with the liberty of others. The ideas expressed in this essay, though not radically divergent from those of his predecessors, are important because they form the basis of the American political system, and are presented by Mill in a fairly accessible manner.