Hank Greenberg's corner office, high in the Park Avenue tower that houses the headquarters of Citigroup, is physically near the heart of the financial world. Until recently, it wasn't obvious that its occupant was near it as well.

Yet Greenberg, at the age of 83, an age when most other former public C.E.O.'s are out on the golf course, has emerged as a central player in the two biggest dramas now playing out in American finance: the shake-up at his former company, insurance giant American International Group, and the battle being fought by Lehman Brothers to remain a thriving independent Wall Street firm.

As A.I.G. stumbled, reporting two consecutive quarterly losses and watching its stock price slide, his guiding spirit and example inspired a shareholder revolt that led to the ouster of Martin Sullivan—Greenberg's one-time protégé—as chief executive.

At the same time, Greenberg's C.V. Starr is among the investors that bought $6 billion of Lehman Brothers' common and preferred stock that is giving the firm—and its embattled chief, Richard Fuld—a badly needed shot in the arm.
 
Lehman, Greenberg told Dow Jones, "is a great franchise overall," giving a clear sign of support for Fuld.

The prominence of Greenberg's role, and the downfall of some past adversaries, most spectacularly his nemesis Eliot Spitzer, must give the insurance titan immense satisfaction even if he won't acknowledge that publicly.

The recent developments involving A.I.G. and Lehman show that while he may no longer have the perks and the huge supporting apparatus of a global public corporation at his disposal, he can still push the levers of power.

"You don't tell the rank of a general by the size of his tent," Greenberg told BusinessWeek in a 2006 interview.

To be sure, the exile of Hank Greenberg has been unlike that of any other departing C.E.O. He has not ridden off into the sunset to tend to his philanthropic causes and his memoirs.

When Greenberg resigned as chief executive and chairman of A.I.G. in March 2005, in the face of investigations by the New York attorney general and the Securities and Exchange Commission, he held the reins of C.V. Starr, a holding company for four insurance agencies with more than $400 million in annual revenue.

And Greenberg has control of some 12 percent of A.I.G.'s shares, giving him more clout than the company's institutional shareholders.

The war against the company he had built began soon after his departure, as A.I.G. and C.V. Starr squabbled and sued each other. It escalated into public criticism of Sullivan and A.I.G. management, even though many of them were once Greenberg's deputies.

In May, Greenberg wrote in a regulatory filing that "A.I.G. is in crisis."

"I am as concerned as millions of other investors as I watch the deterioration of a great company," he said.

It was Sullivan's misplaced confidence in the firm's valuation of credit investments in its portfolio, the subsequent $20 billion in write-downs, and a sinking stock price that led to his ouster on Sunday.

Yet it is also easy to believe that even if Sullivan had not stumbled in the credit crisis, and if he had somehow, after resolving the insurance giant's regulatory problems, been able to push its stock price back up to its pre-Spitzer levels, Greenberg might still be grumbling.

As a self-made man who built A.I.G. into a global giant in insurance over the course of four decades, it is understandably difficult for Greenberg to let go. (He has said, however, that he does not want to return to A.I.G. as an officer or director.)

The legendary drive of Greenberg is matched only by his feistiness. This World War II and Korean War veteran is famous for being a taskmaster, shouting at executives even when they were his sons.

And he has not stayed quiet, even when it was in his best interest to do so. He has been outspoken about A.I.G.; the New York attorney general still has a lawsuit against him; and the Securities and Exchange Commission is reportedly investigating his role in two transactions at A.I.G.

After the A.I.G. board meeting on Sunday, the new chief executive, Robert Willumstad, reached out to Greenberg, the Wall Street Journal reports, but did not speak with him.

Perhaps Greenberg is still not satisfied.