One of the drawbacks to having superhuman skills is that you tend to attract equally well-enabled arch-enemies. And Greenberg's bête noir is unquestionably Eliot Spitzer. In a 12-month span that became Greenberg's annus horribilis, an investigation by then-N.Y. Attorney General Spitzer into a kickback scheme involving Marsh & McLennan culminated in October 2004 with the ouster of his son, Jeffrey, as Marsh's CEO.

Then an even bigger blow soon followed: A Spitzer-led inquiry into AIG's finances led to the discovery of a "phantom" $500-million reinsurance deal with GenRe, a unit of Warren Buffett's Berkshire Hathaway, which ultimately resulted in AIG's board of directors calling on Greenberg to step down, which he did on March 15, 2005. While all criminal charges against Greenberg were dropped, the State of New York is continuing to pursue a civil case against him for fraudulently inflating reserves.

But in a backhanded compliment to his nemesis, even Spitzer concedes that Greenberg was a breed apart. In the movie "Client 9: The Rise and Fall of Eliot Spitzer"—a documentary looking at his own fall from power due to a prostitution scandal—Spitzer says of Greenberg: "He was Louis XIV to everybody else's being a mere baron. Hank Greenberg epitomized the power of CEOs, and in my view, he was the most powerful person in corporate America."