Sir Karl Raimund Popper, CH FRS FBA (28 July 1902 – 17 September 1994) was an Austro-British philosopher and a professor at the London School of Economics. He is regarded as one of the greatest philosophers of science of the 20th century; he also wrote extensively on social and political philosophy.
Popper is known for his attempt to repudiate the classical observationalist / inductivist form of scientific method in favour of empirical falsification. He is also known for his opposition to the classical justificationist account of knowledge which he replaced with critical rationalism, "the first non justificational philosophy of criticism in the history of philosophy". As well, he is known for his vigorous defense of liberal democracy and the principles of social criticism that he came to believe made a flourishing "open society" possible.