The influential political thinker who wrote "The Social Contract," advocating for the understanding of political legitimacy, was Jean-Jacques Rousseau. In this seminal work, Rousseau posited that legitimate political authority stems from a contract between the governed and the government, emphasizing the importance of general will and collective sovereignty. His ideas significantly influenced democratic principles and revolutionary thought, advocating for individual freedom and direct participation in governance. Rousseau's theories laid the groundwork for modern political philosophy, urging societies to align governance with the values and needs of the populace.