(Sir) Karl Popper
Karl Popper was one of the greatest philosophers of the Twentieth Century. He is arguably best known for his Philosophy of Science - which is founded on Falsificationism - the idea that the theories of sciences are not in any sense "confirmed" (proved to be "true" - Verificationism) but rather falsified during their proving. But he is also known for his championing of Realism in Ontology and Fallibilism in Epistemology.
...and here is the Wikipedia entry: Karl Popper.
Here is what Stephen J. Gould chooses to quote about Falsificationism: Science as Falsification and many of his works, including "Conjectures and Refutations" are discussed on [www.tkpw.net The Karl Popper Web]
STREAMS takes from Karl Popper not only his Realism but specifically his "Three Worlds" Ontology, Epistemic Fallibilism - and much of his Philosophy of Science.