Paul O'Neill, a former Treasury Secretary under President George W. Bush, has died age 84 after battling lung cancer, his family announced Saturday.

His son Paul Jr. confirmed that his father died at his home in Pittsburgh after deciding against any further intervention and treatment four or five months ago.

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“There was some family here and he died peacefully,” he said, according to the Associated Press. “Based on his situation it was a good exit.”

O'Neill was a former chairman of aluminum giant Alcoa, the world's biggest aluminum manufacturer, and caused controversy when he took the job of Treasury chief in 2001, announcing that he would keep nearly $100 million worth of stock in the company. He eventually reversed that decision amid criticism about a potential conflict of interest.

But controversy dogged him during his tenure, particularly because of his blunt speaking style. In the spring of 2001 after the Dow suffered its worst week of declines in 11 years, he declared that "markets go up and markets go down." After the 9/11 attacks, he downplayed the idea that the economy was going into recession -- something it later did.

He resigned in late 2002 after objecting to another round of Bush tax cuts. He later worked with author Ron Suskind on a book covering his two years in the administration.

The book, "The Price of Loyalty: George W. Bush, the White House and the Education of Paul O’Neill” was critical of the administration and contended that the administration began planning the overthrow of Iraq President Saddam Hussein right after Bush took office, eight months before the Sept. 11 terrorist attacks.

Then U.S. Secretary of Treasury Paul O'Neill points to a reporter during a post G-7 news conference at the World Bank Building in Washington, U.S., September 28, 2002. (Reuters)

The book depicted Bush as a disengaged president, and that decisions were often made by Bush's political team and Vice President Dick Cheney -- who O'Neill had been recruited by to join the Cabinet.

After leaving office, O'Neill resumed working with the Pittsburgh Regional Health Care Initiative, a consortium of hospitals, medical societies and businesses studying ways to improve health care delivery in Western Pennsylvania.

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He also devoted time in retirement to projects that would deliver clean drinking water to Africa. As Treasury secretary, O’Neill had focused attention on poverty and combating diseases such as AIDS in Africa, touring the continent with Irish rock star Bono.

The Associated Press contributed to this report.