One of the eminent economists of the 20th century, he is known for his disagreements with Keynes, believing that to keep unemployment low would call for growing inflation. We teach this as the Phillips Curve. He was also a member of the Austrian School - the only major member of that school who was actually born and raised in Austria (according to this source).
You can learn more about him here. And if you haven't seen it, you can "watch" him debate Keynes in "Fear the Boom and Bust."