Hans Kelsen was an influential Austrian jurist and legal philosopher, born on October 11, 1881. He is best known for developing the Pure Theory of Law, which emphasizes the separation of law from morality and politics. Kelsen argued that law should be understood as a system of norms, focusing on its structure rather than its social or ethical implications. Kelsen's work significantly impacted legal theory and constitutional law, particularly through his contributions to the Austrian Constitution of 1920. His ideas have influenced various legal systems worldwide, and he is often regarded as one of the most important figures in modern legal philosophy.