Hugo Grotius was a Dutch philosopher, lawyer, and diplomat born in 1583. He is often referred to as the "father of international law" for his influential work in establishing principles that govern relations between nations. His most famous book, De Jure Belli ac Pacis, laid the groundwork for modern legal frameworks concerning war and peace. Grotius believed in the importance of natural law, which suggests that certain rights and moral principles are inherent to all humans. His ideas have significantly shaped international relations and legal thought, influencing later thinkers like John Locke and Immanuel Kant.