5. John Arnold
John Arnold
Founder, Centaurus Energy
Age: 37
Industry: Finance

The trading star who cut his teeth at Enron turned a talent for reading the notoriously fickle gas markets into an estimated $4 billion hedge fund fortune. He's bounced back from his first-ever down year, with his flagship fund up about 4%, and invests in natural-gas storage caverns and power plants, turning Centaurus into a diversified energy firm some have likened to a mini-Enron. Billionaire props include an art-filled modernist mansion in Houston and a foundation to support overhauling America's pension system.

Spare time: Arnold is said to be a Dave Matthews and U2 fan.


Last updated October 25 2011: 5:11 PM ET
Join the Conversation
Ones to watch

In addition to Fortune's 40 Under 40 list, we're also keeping our eye on these 20 innovators, young guns from a wide range of industries and backgrounds.

Video

Most stock quote data provided by BATS. Market indices are shown in real time, except for the DJIA, which is delayed by two minutes. All times are ET. Disclaimer.

Morningstar: © 2014 Morningstar, Inc. All Rights Reserved.

Factset: FactSet Research Systems Inc. 2014. All rights reserved.

Chicago Mercantile Association: Certain market data is the property of Chicago Mercantile Exchange Inc. and its licensors. All rights reserved.

Dow Jones: The Dow Jones branded indices are proprietary to and are calculated, distributed and marketed by DJI Opco, a subsidiary of S&P Dow Jones Indices LLC and have been licensed for use to S&P Opco, LLC and CNN. Standard & Poor's and S&P are registered trademarks of Standard & Poor’s Financial Services LLC and Dow Jones is a registered trademark of Dow Jones Trademark Holdings LLC. All content of the Dow Jones branded indices © S&P Dow Jones Indices LLC 2014 and/or its affiliates.