Peter L. Bernstein, the author of Against the Gods: The Remarkable Story of Risk and other books, died on June 5th at the age of 90. In this McKinsey Quarterly video from January 2008, the well-known author discusses the meaning of risk and explains why sophisticated mathematical models to control it sometimes go awry.

Ultimately, Peter L. Bernstein will be remembered for his development and refinement of efficient market theory, which helped him bring investing theory -- more than simply picking stocks -- to the general public. Bernstein, it seems, advocated increased regulatory oversight to strengthen the foundation of the markets, while also believing that the wealth and opportunity created by a free market were worth the risk. He also was a Keynesian and he argued that the health of the market economy required public spending on various projects.