WASHINGTON (AP) — Dick Cheney, the hard-charging conservative who became one of the most powerful and polarizing vice presidents in U.S. history and a leading advocate for the invasion of Iraq, has died at 84.

Cheney died Monday due to complications of pneumonia and cardiac and vascular disease, his family said Tuesday.

The quietly forceful Cheney led the armed forces as defense secretary during the Persian Gulf War under President George H.W. Bush before returning to public life as vice president under Bush’s son George W. Bush.

Cheney was, in effect, the chief operating officer of the younger Bush’s presidency. He often had a commanding hand in implementing decisions most important to the president and some of surpassing interest to himself — all while living with decades of heart disease and, post-administration, a heart transplant. Cheney consistently defended the extraordinary tools of surveillance, detention and inquisition employed in response to the Sept. 11, 2001, attacks.

“History will remember him as among the finest public servants of his generation — a patriot who brought integrity, high intelligence, and seriousness of purpose to every position he held,” Bush said.

Years after leaving office, Cheney became a target of President Donald Trump, especially after his daughter Liz Cheney became the leading Republican critic and examiner of Trump’s attempts to stay in power after his 2020 election defeat and his actions in the Jan. 6, 2021, Capitol riot.

Cheney said last year he was voting for Democrat Kamala Harris for president against Trump.

For all his conservatism, Cheney was privately and publicly supportive of his daughter Mary Cheney after she came out as gay, years before same-sex marriage was broadly supported. “Freedom means freedom for everyone,” he said.

In his time in office, no longer was the vice presidency merely a ceremonial afterthought. Instead, Cheney made it a network of back channels from which to influence policy on Iraq, terrorism, presidential powers and energy.

A hard-liner on Iraq, Cheney was proved wrong about the rationale for the Iraq War, a point he didn't acknowledge.

He alleged links between the 9/11 attacks and prewar Iraq that didn’t exist. He said U.S. troops would be welcomed as liberators; they weren’t.

He declared the Iraqi insurgency in its last throes in May 2005, when 1,661 U.S. service members had been killed, not even half the toll by the war’s end.

Cheney and Bush struck an odd bargain, unspoken but well understood. Shelving ambitions he might have had to succeed Bush, Cheney was accorded extraordinary power.

His penchant for secrecy had a price. He came to be seen as a Machiavelli orchestrating a bungled response to criticism of the Iraq War. And when he shot a hunting companion with an errant shotgun blast in 2006, he and his coterie were slow to disclose that episode. The victim, his friend Harry Whittington, recovered and forgave him.

Bush asked Cheney to lead a search for his vice president, eventually deciding the job should go to Cheney himself. Their election in 2000 was ultimately sealed by the Supreme Court after a protracted legal fight.

On Capitol Hill, Cheney lobbied for the president’s programs where he had once served as a deeply conservative member of Congress and the No. 2 Republican House leader.

On Sept. 11, 2001, with Bush out of town, the president gave Cheney approval to authorize the military to shoot down hijacked planes. By then, two airliners had hit the World Trade Center and a third was bearing down on the capital. A Secret Service agent burst into the West Wing room, grabbed Cheney by the belt and shoulder and led him to a bunker underneath the White House.

Cheney's career in Washington started with a congressional fellowship in 1968. He became a protégé of Rep. Donald Rumsfeld, R-Ill., serving under him in Gerald Ford’s White House before he was elevated to chief of staff, the youngest ever, at age 34.

He later returned to Casper, Wyoming, and won the state's lone congressional seat, the first of six terms.

In 1989, Cheney became defense secretary and led the Pentagon during the 1990-91 Persian Gulf War. Between the two Bush administrations, Cheney led Dallas-based Halliburton Corp., an oil industry services company.

Cheney was born in Lincoln, Nebraska, son of a longtime Agriculture Department worker. Senior class president and football co-captain in Casper, he went to Yale on a full scholarship for a year but failed out.

He moved back to Wyoming and renewed a relationship with high school sweetheart Lynne Anne Vincent, marrying her in 1964. He is survived by his wife and daughters.

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Associated Press writer Mead Gruver in Cheyenne, Wyo., contributed.