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Richard Posner

Age: 75

Occupation: Judge, U.S. Court of Appeals, 7th Circuit

This federal judge is the most cited legal scholar of the 20th century, having published some 2,500 articles and 30 books, including 2013’s Reflections on Judging. Mind you, he squeezes this in when not writing for The New Republic, Slate, or his blog with colleague Gary Becker.