There were many sides to Ibn Khaldun - a top scholar, a scheming political mastermind, a peripatetic political guru to many a dynasty in North Africa, an inventor of a social science or two. He also spent a month talking to one of the world’s most dangerous conquerors and was imprisoned several times. At a time when the Black Death was raging through the area he suffered terrible personal tragedies. One of his books, the Muqaddimah, is now regarded as a classic text. And how many historians from the Middle Ages have come up with theories that are invoked by modern-day economists and American presidents?

(Image: Drawing of Ibn Khaldun on a 10 Dinar Tunisian banknote. Credit Georgios Art/Getty Images)