People love lists: the Ten Commandments, the Seven Deadly Sins, and the Four Beatles. But they are fascinated by rankings, which are lists organized according to some measure of value or merit. Who were the most important women in history? The best writers or most influential artists? Our least illustrious presidents? Who's bigger: John, Paul, George, or Ringo?

This is a book about measuring the “significance” of historical figures. We do not answer these questions as historians might, through a principled assessment of their individual achievements. Instead, we evaluate each person by aggregating the traces of millions of opinions in a rigorous and principled manner. We rank historical figures just as Google ranks web pages, by integrating a diverse set of measurements about their reputation into a single consensus value.

Significance is related to fame but measures something different. Forgotten U.S. president Chester A. Arthur (1829–1886) [499] is more historically significant than young pop singer Justin Bieber (1994–) [8633], even though he may have a less devoted following and lower contemporary name recognition. Significance is the result of social and cultural forces acting on the mass of an individual's achievement. We think you will be impressed by the extent to which our results capture what you think of as “historical significance.” And our computational, data-centric analysis provides new ways to understand and interpret the past.