Pierre Joseph Proudhon was a French philosopher and politician who is known for his influential works on political theory and economics. He is often considered the father of anarchism and is famous for his statement "Property is theft!" Proudhon's ideas on mutualism, federalism, and the role of the state in society have had a lasting impact on political and economic thought. He was a prolific writer and his works continue to be studied and debated by scholars and activists around the world.