The key philosopher behind the idea of the social contract was Jean-Jacques Rousseau. In his influential work "The Social Contract" (1762), Rousseau proposed that legitimate political authority arises from an agreement among individuals to form a society. He argued that in a state of nature, individuals are free and equal, but the formation of societies and governments often leads to inequality and oppression. Rousseau believed that people must collectively agree to create laws and institutions that reflect the general will, promoting freedom and equality. His ideas significantly influenced modern political philosophy, shaping concepts of democracy, citizenship, and civil rights.