When Maurice R. "Hank" Greenberg ran American International Group Inc., the insurance giant was known for its acumen for spotting weaknesses in rivals.

Now, Mr. Greenberg is attempting to use similar tactics on AIG itself.

By declaring his interest on Friday to look for "strategic alternatives," he threw down the gauntlet about the direction of AIG — a company he led for decades before retiring in 2005 amid an accounting scandal.

AIG and Mr. Greenberg, 82 years old, have been duelling ever since his departure. The two sides have lawsuits pending against each other relating to stewardship of the company.

Investors are jittery. AIG shares fell more than eight percent in midday trading one day last month, before largely bouncing back. Much of their nervousness stems from potential exposure to the subprime mortgage market. AIG is scheduled to report third-quarter earnings tomorrow.

While Mr. Greenberg's move could offer dissatisfied shareholders a rallying point, his ultimate goals are shrouded in mystery. A number of scenarios is possible, including a move to invite bidders for the company, a breakup or spinoff of some of its assets, or perhaps a public campaign against the company's top management.

Mr. Greenberg made his statements in a 13D filing to the Securities and Exchange Commission. Such a filing doesn't commit a filer to a specific action. An attorney for Mr. Greenberg declined to comment on Sunday.

The filing throws a spotlight on the ability of AIG's current CEO, Martin Sullivan — Mr. Greenberg's one-time deputy — to manoeuvre the current housing-market turmoil. It is the kind of market environment the entrepreneurial Mr. Greenberg likely would have embraced in his tenure at AIG by seeking out beaten-down investments.

At the same time, Mr. Greenberg is contending with legal matters related to his tenure at the firm. His retirement in 2005 accompanied intense scrutiny of AIG due to state and federal investigations into its accounting. AIG later paid $1.6 billion in a settlement.

It isn't clear if a significant number of other shareholders would join Mr. Greenberg and his allies, who together held 13.6 percent of AIG's shares at the time of a March filing. Two of the other filers are companies Mr. Greenberg leads. Both have sold off some of their holdings in AIG since he left.

The probability that AIG's management could be overthrown isn't "that high," says Thomas Vandeventer of New York-based Tocqueville Asset Management. In comparison with Citigroup Inc., whose chief executive, Charles Prince, resigned Sunday, "Investors are probably going to be more patient with an AIG."

AIG's current CEO, Mr. Sullivan, guided the company through the tumultuous period that led up to the accounting-scandal settlement in early 2006. In recent quarters he has piloted it to strong profit growth, including a 34 percent increase in profit in the second quarter.

Still, for the past couple years, the stock has largely traded in a range between the high 50s and the low 70s. Shares closed at $59.12 Friday, giving it a market capitalization of $151.6 billion.

That is one indication that there are questions about whether the company should enjoy a premium on its share price the way it did at times under Mr. Greenberg.

Mr. Vandeventer says that key questions are, "How good is the business, really?" and is Mr. Sullivan "the guy who can lead it" given that he hasn't yet led the insurer all the way through one of the perilous pricing cycles that routinely strike the industry.

Mr. Vandeventer says he has been trimming the AIG stakes held by the funds at his firm in the past three or four years.

Under Mr. Sullivan, AIG has also pushed into markets that hold the potential for high growth, including China, Vietnam and Japan.

In an interview last month, Mr. Sullivan portrayed the firm as poised to take advantage of any opportunities that might arise from the current US market turmoil.

"Have the fishing rod ready, but make sure you're not casting out too soon, or more importantly, too late," he said.

At that time, he said his "current view" was that opportunities would arise in the investment arena sooner than in the housing market, in the next three to six months.

Mr. Sullivan was on a business trip in the UK when Mr. Greenberg's filing landed on Friday. That evening, New York time, an AIG spokesman released a statement saying the firm "has made tremendous progress over the past 2 ½ years and has established a strong culture of good corporate governance. The company is pursuing the right strategies, and the board and management are united in their commitment to building shareholder value."

AIG had "no indication" that Mr. Greenberg was going to make the filing, an AIG spokesman said on Sunday. "Nor are we aware of any other investors being involved," said the spokesman, Chris Winans.

Mr. Greenberg and AIG have a colourful, contentious relationship. Shortly after his departure, the two sides argued about property that Mr. Greenberg wanted returned to him, including works of art including a Van Gogh, and also letters sent to him by his mother decades ago. This year, AIG sued Mr. Greenberg and another former top executive in Delaware's Court of Chancery for $1 billion in damages related to the accounting troubles at AIG.

Days later, Mr. Greenberg filed suit against the company, accusing its directors of "seriously damaging" the firm. Other legal matters are pending.

Mr. Greenberg is fighting civil charges by the New York State Attorney General's office related to his time at the helm of AIG, although many of those charges have been dropped. AIG is also still disputing control of the shares held by one of the firms that joined Mr. Greenberg in the filing, Starr International Co., which he heads.

In September Mr. Greenberg's attorney said his client had received a subpoena from the SEC and agreed to testify later that month.

When Mr. Greenberg appeared he refused to answer some questions citing his Fifth Amendment right against self-incrimination, according to people familiar with the matter. An attorney for Mr. Greenberg declined to comment.

In an interview before the recent lawsuits involving him and AIG were filed, Mr. Greenberg described his feelings about the firm in dispassionate terms, saying, "I think AIG has a great franchise, which I think I helped build. It depends how the franchise is used. That will determine the future. I hope it does well. And if it doesn't, I'll be just another investor and decide as an investor should."

AIG shares long traded at a hefty premium under Mr. Greenberg. But the company is now already one of the largest in the world. Prices are falling in many key lines of insurance, as the industry goes through its characteristic price cycle. And competition among insurers is intense.

With its sprawling operations in more than 100 countries, and businesses that range well beyond insurance to lending and leasing aircraft, AIG can also be tough for some investors to understand. To date, there have been no widespread public complaints about the way the company is investing its capital, or about Mr. Sullivan's leadership.

Some analysts who have been trying to calculate AIG's possible risk from the subprime market believe it is likely to be manageable, and that concerns about the issue may be exaggerated.