US Senator John McCain, the 2008 Republican presidential nominee who was driven by a code of honour that defined and haunted him, has died at 81.

McCain endured more than five years of imprisonment and torture by the North Vietnamese as a young Navy pilot.

He went on to battle foes — on the left and the right — in the marble corridors of Washington.

A Republican who seemed his truest self when outraged, he reveled in opposing orthodoxy and spent decades representing Arizona in the Senate.

He twice ran unsuccessfully for president. McCain was diagnosed with a brain tumour in July 2017.

.@SenJohnMcCain May you rest in some well-deserved peace after a lifetime of fighting for us, sir.

— Jennifer Granholm (@JenGranholm) August 26, 2018

I will never forget a debate in Arizona, where Sen McCain spent the evening joking with Barbara and me. We were nervous for our dad, he felt it and he was kind. In the cold world of politics, he was a bright light. Prayers to his family.

— Jenna Bush Hager (@JennaBushHager) August 26, 2018

So much of our politics has been impoverished by insincere conversations among Baby Boomers. Too little has been informed by the sacrifices of those who paid the price for decisions of the past. John S. McCain, R.I.P.

— Chris Stirewalt (@ChrisStirewalt) August 26, 2018

John McCain, an American original, dies at age 81 https://t.co/atWEVpOXo7

— TIME (@TIME) August 26, 2018

RIP John McCain, American hero, two-time presidential candidate and towering figure in modern times. https://t.co/JExr37Xpqr

— Peter Baker (@peterbakernyt) August 26, 2018

We remember Sen. #McCain as a selfless patriot who put family and country first. He honored his family’s military service with not only words, but deeds, serving bravely in Vietnam. Sen. McCain’s collaboration in Congress should be a model for all. We’ve lost a national treasure.

— Rep. Eric Swalwell (@RepSwalwell) August 26, 2018

We remember Sen. #McCain as a selfless patriot who put family and country first. He honored his family’s military service with not only words, but deeds, serving bravely in Vietnam. Sen. McCain’s collaboration in Congress should be a model for all. We’ve lost a national treasure.

— Rep. Eric Swalwell (@RepSwalwell) August 26, 2018