Last month, 40 billionaires from around the United States announced that they had signed “The Giving Pledgecis,” an initiative started by Warren Buffett and Bill and Melinda Gates, stating their plans to donate the majority of their personal fortunes in their lifetime or after their death. Among the other signers are Star Wars director George Lucas, New York City Mayor Michael Bloomberg, and Texans T. Boone Pickens and Laura and John Arnold, who made their money through natural gas trading with John’s Houston-based hedge fund Centaurus Energy.