John Stuart Mill introduced significant philosophical ideas, particularly those concerning utilitarianism and liberty. In his work "On Liberty," Mill emphasized the importance of individual freedom and the need to protect minority opinions against the tyranny of the majority. His concept of harm principle argued that actions should only be limited to prevent harm to others. Additionally, Mill's advocacy for women's rights and educational access highlighted his progressive views for his time. Through his essays and writings, Mill laid the groundwork for discussions on personal liberties, ethics, and social justice, influencing modern liberal thought.