Donald Rumsfeld, the two-time US defence secretary and one-time presidential candidate, has died at the age of 88, his family said in a statement.
The family said he “was surrounded by family in his beloved Taos, New Mexico”.
Mr Rumsfeld was regarded by former colleagues as smart and combative, patriotic and politically cunning, and had a storied career under four presidents and nearly a quarter of a century in corporate America.
But his reputation as a skilled bureaucrat and visionary of a modern US military was soiled by the long and costly Iraq war.
In 2001 he began his second tour as Pentagon chief under George W Bush, but his plan to “transform” the armed forces was overshadowed by the September 11 terrorist attacks.
He oversaw the US invasion of Afghanistan and the 2003 overthrow of Saddam Hussein in Iraq, where he was blamed for setbacks including the Abu Ghraib prisoner abuse scandal and for being slow to recognise a violent insurgency.
After retiring in 2008 he headed the Rumsfeld Foundation to promote public service and to work with charities that provide services and support for military families and wounded veterans.
Rummy, as he was often called, was ambitious, witty, energetic, engaging and capable of great personal warmth, but he irritated many with his confrontational style. An accomplished wrestler in college, he relished verbal sparring and elevated it to an art form, and a biting humour was a favourite weapon.
He built a network of loyalists who admired his work ethic, intelligence and impatience with all who failed to share his sense of urgency.
Mr Rumsfeld is the only person to serve twice as Pentagon chief. The first time, in 1975-77, he was the youngest ever. The next time, in 2001-06, he was the oldest.
He made a brief run for the 1988 Republican presidential nomination, a spectacular flop he described as humbling for a man used to success at the highest levels of government, including stints as White House chief of staff, US ambassador and member of Congress.
For all his achievements, it is the setbacks in Iraq in the twilight of his career that are likely to be the most vivid features of his legacy.
Nine months into his second tour as defence secretary, on September 11 2001, suicide hijackers attacked the World Trade Centre in New York and the Pentagon, thrusting the nation into wars for which the military was ill-prepared.
Mr Rumsfeld oversaw the US invasion of Afghanistan and toppling of the Taliban regime. Frequently presiding at televised briefings on the war, he became something of a TV star, applauded for his blunt talk and uncompromising style.
By 2002 the Bush administration’s attention shifted to Iraq, which played no role in the September 11 attacks. The war effort in Afghanistan took a back seat to Iraq, opening the way for the Taliban to make a comeback and prevent the US from sealing the success of its initial invasion.
The US-led invasion of Iraq was launched in March 2003. Baghdad fell quickly, but US and allied forces soon became consumed with a violent insurgency. Critics faulted Mr Rumsfeld for dismissing the pre-invasion assessment of the army’s top general, Eric Shinseki, that several hundred thousand allied troops would be needed to stabilise Iraq.
Mr Rumsfeld twice offered his resignation to President Bush in 2004 amid disclosures that US troops had abused detainees at Iraq’s Abu Ghraib prison — an episode he later referred to as his darkest hour as defence secretary.
Not until November 2006, after Democrats gained control of Congress by riding a wave of anti-war sentiment, did Mr Bush finally decide Mr Rumsfeld had to go. He left office in December, replaced by Robert Gates.
Mr Rumsfeld is survived by his wife Joyce, three children and seven grandchildren.