An in-depth profile of Laura and John Arnold, part of new wave of philanthropists who want to use "data analysis and science" to mitigate society's ills.

"Arnold, it turns out, had accumulated a fortune estimated at $4 billion in the past decade—only a handful of people on Wall Street made more during that time. Although he had not yet announced it, Arnold had decided to give almost all of it away. In October 2012, he closed his hedge fund, Centaurus Energy, and retired. In U.S. history, there may have never been a self-made individual with so much money who devoted himself to philanthropy at such a young age." -- Brad Reagan, the Wall Street Journal