But comments made by Adam Tan, HNA’s chief executive, deepened the mystery of who really owned Mr. Guan’s stake. Speaking to The Financial Times on Monday, he said that Mr. Guan, and another shareholder, Bharat Bhise, who had transferred much of his stake to Mr. Guan last year, had never actually owned the shares at all, “but had just held the stake for us,” Mr. Tan told the newspaper.
At first glance, it appears to be one of the most generous donations in the history of philanthropic giving in America.
A Chinese man has transferred more than 29 percent of HNA Group of China — the equivalent of as much as $18 billion — to a New York-based private foundation. The donation puts him in the same league as donors like Bill Gates and Warren E. Buffett and almost matched the combined giving of all American corporations in 2016.
But it has not been disclosed how that man, Guan Jun, who is in his 30s, came to own such a large piece of one of China’s biggest conglomerates. His registered address in Beijing is a modest apartment at the end of a dingy hallway littered with discarded furniture and bags of trash.
Questions about Mr. Guan, who could not be reached for comment, and the foundation have mounted since HNA disclosed on Monday the donation to the New York-based Hainan Cihang Charity Foundation, which aims to support a variety of causes including anti-poverty efforts. Little is known about Mr. Guan, though he is a director in a company whose address is in the HNA building in Beijing.
That has never been disclosed in regulatory filings, which had listed the two as the owners of the shares. Mr. Tan himself, along with Chen Guoqing, the brother of Chen Feng, HNA’s chairman, were the original owners of Tang Dynasty, a Hong Kong holding company that is a large shareholder in HNA’s complex web of ownership.
Understanding HNA’s ownership structure is important because the company last year was the biggest Chinese investor in the United States. Many companies, including banks, are bound by know-your-customer rules and need clarity on who owns their clients’ business. Bank of America recently decided not to engage in any transactions with the Chinese conglomerate, citing concerns over its murky shareholder structure and allegations of political connections.
The decision to transfer Mr. Guan’s stake to the foundation, HNA said, was to allay concerns over its shareholding. Scrutiny of its ownership had escalated after Anthony Scaramucci, the new White House communications director, announced in January that he was selling his hedge fund to an HNA subsidiary.
Instead, HNA, in making the unusual decision to transfer such a large portion of its ownership to an American foundation, raises questions about how it will comply with United States tax law.
Federal laws in place for almost half a century, meant to keep the wealthy from using foundations as a tax shelter, generally restrict foundations from owning more than 20 percent of a company, though there are exceptions that may apply to HNA. Under the law, that percentage can be reduced much further, to as low as 2 percent, if major shareholders have a hand in running the foundation, tax lawyers say.
The Chinese branch of Hainan Cihang owns an additional 22.8 percent, bringing the total owned by the foundations to about 52 percent.
Foundations have five years to comply, and are often given five years on top of that, which gives them time to dispose of their excess holdings, tax experts say. But after that, penalties are severe — a 10 percent tax on the excess holdings followed by a 200 percent follow-on tax on the excess amount if the holdings remain out of compliance.
“Sooner or later you’re going to have to get rid of your excess business holdings or your foundation is going to be handed over to the I.R.S.,” said Richard Schmalbeck, a law professor at Duke University who focuses on nonprofit organizations.
Hainan Cihang also must begin distributing 5 percent of its assets every year.
According to figures derived from the privately held company’s 2016 annual report, HNA’s book value is $61 billion, making Hainan Cihang’s share worth $18 billion. That translates into $900 million in donations a year, which may necessitate assets sales in order to raise that money, Mr. Schmalbeck said.
“This could be a real painful box for them to be in,” he said.
Allen Wu, a lawyer in New York representing Hainan Cihang, did not return two phone calls seeking comment.
One person briefed on the matter said that the asset value transferred from HNA to the charity was still not settled and would likely be considerably smaller than $18 billion.
Hainan Cihang is likely to support causes such as refugee aid, food aid, free cataract surgery and women’s issues, said the person, who requested anonymity because the foundation’s plans have not been finalized.
The person briefed on the matter added that the foundation was applying for tax-exempt status with the Internal Revenue Service and that it would be disclosing more information in the future. For now, a 2016 tax year filing to the I.R.S. shows it has no assets. The foundation has registered with the New York State Department of State.
HNA’s murky ownership structure and huge transfer to a private foundation hark back to an earlier era in the United States, when rich families would often put assets into foundations to shield them from taxation. A 1969 law changed that, instituting the 20 percent cap and the requirement to give out 5 percent of the holdings each year.
“The concern was that if private foundations owned large amounts of a business, then the trustees of the foundation could become more concerned with the interests of the business,” said Ray Madoff, a law professor at Boston College who focuses on philanthropies and taxes.
HNA, which has been a deal-making juggernaut in recent years, has lately run into roadblocks both in China, where officials are trying to slow the outflow of foreign currency reserves, and in Washington.
Mr. Scaramucci’s sale of his ownership in SkyBridge Capital, his hedge fund of funds business, has not yet been cleared by Cfius. In January, Mr. Scaramucci announced that he had sold Skybridge to a consortium led by RON Transatlantic and HNA Capital, an arm of HNA Group.
Rich Myers, a spokesman for Skybridge, said on Wednesday that the deal had cleared all other hurdles and that the company was confident it would have approval from the Committee on Foreign Investment in the United States, which reviews acquisitions and investments for national security risks, by the end of the summer.
Earlier this year, at a hedge fund conference where he once played host, Mr. Scaramucci called HNA “one of the more magnificent conglomerates coming out of China.” He also encouraged the audience, gathered at the Bellagio Hotel in Las Vegas, to get to know Guang Yang, the chief executive of HNA Capital, who was also in attendance.
Mr. Scaramucci did not respond to an email requesting comment on Wednesday.
Regulators may also want to get to know Mr. Yang. He is the person who signed Hainan Cihang’s annual return filed to the I.R.S.