John Stuart Mill 
Utilitarianism 

The book explains what utilitarianism is, why it is the best theory of ethics, defends it against a wide range of criticisms and misunderstandings. Though heavily criticized both in Mill’s lifetime and in the years since, Utilitarianism did a great deal to popularize utilitarian ethics and was 'the most influential philosophical articulation of a liberal humanistic morality that was produced in the nineteenth century.’