Karl Popper was a prominent 20th-century philosopher known for his contributions to the philosophy of science. He is best known for his principle of falsifiability, which asserts that for a theory to be considered scientific, it must be testable and refutable. This idea challenged the traditional view of science and emphasized the importance of skepticism in scientific inquiry. Popper's work extended beyond science to include political philosophy, where he advocated for open societies and criticized totalitarianism. His influential books, such as The Logic of Scientific Discovery and The Open Society and Its Enemies, continue to shape discussions in both science and philosophy today.