Rudolf Carnap
He played a most conspicuous role in the movement of Vienna Circle (logical empiricism). He studied mathematics, physics and philosophy in Jena; he was one of the very few students of Frege. After obtaining his doctorate in philosophy with the thesis Der Raum, he joined the Vienna Circle in 1926; his first major work Der logische Aufbau der Welt (1928) established his reputation as a logical empiricist.
In 1936 he moved into the United States, and taught at Chicago, and after Reichenbach's death, at Los Angeles. His contributions to logical semantics, philosophy of science in general, philosophy of space, philosophy of probability and induction are very important. Quine, for instance, formed his own philosophical thoughts in opposition to Carnap's.
See also "Carnap" in Internet Encyclopedia of Philosophy