AGE: 73 OCCUPATION: Judge, United States Court of Appeals

Averaging a book a year for the past 40 years while also teaching at the University of Chicago and holding down his day job with distinction, Posner ranks as one of the nation’s top thinkers. According to Yale legal scholar Fred Shapiro, Posner is the most cited jurist of the 20th century.

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Photograph: Milbert Orlando Brown/Chicago Tribune