Former US Vice-President Dick Cheney, a key architect of George W Bush's 'war on terror' and an early advocate of the invasion of Iraq in 2003, has died at the age of 84.

He died from complications of pneumonia and cardiac and vascular disease on Monday night, his family said.

Cheney served as Gerald Ford's White House chief of staff in the 1970s, before later becoming one of the most powerful US vice presidents in history under Bush.

In his later years, he became a bitter critic of the Republican party under the leadership of Donald Trump.

Dick Cheney was a great and good man who taught his children and grandchildren to love our country, and to live lives of courage, honour, love, kindness, and fly fishing, his family said in a statement.

Cheney was born in Lincoln, Nebraska in 1941, and later attended the prestigious Yale University on a scholarship but failed to graduate. He went on to gain a Master's degree in political science from the University of Wyoming.

His first taste of Washington came in 1968, when he worked for William Steiger, a young Republican representative from Wisconsin. Cheney became chief of staff under Ford when he was just 34, before spending a decade in the House of Representatives.

As secretary of defence under George Bush Snr, he presided over the Pentagon during the 1990-91 Gulf War, in which a US-led coalition evicted Iraqi troops from Kuwait. He then became VP to George W Bush in 2001 and played a greater role in making major policy decisions than most of his predecessors.

Despite decades of working for Republican presidents, he later became a bitter opponent of President Donald Trump. Having initially endorsed him in 2016, Cheney was appalled by allegations of Russian interference in the presidential election and Trump's seemingly casual attitude towards NATO.

Cheney's key role in the campaign heavily affected his political legacy, after the US took years to extricate itself from its costly war in Iraq, resulting in the deaths of hundreds of thousands of people.

In an odd final twist, his own Trump criticism would win him praise from some on the left who had once denounced him decades earlier.