Politicians from around the world have paid warm tribute to former Foreign Secretary Robin Cook after his death.
Mr Cook collapsed while hill walking in north-west Scotland. The 59-year-old resigned from the Cabinet in 2003 over the Iraq war.
Tony Blair called Mr Cook "an outstanding, extraordinary talent".
Tory leader Michael Howard praised his "immense" contribution to UK politics. Lib Dem leader Charles Kennedy said he was "deeply saddened".
Mr Cook was with second wife Gaynor when he was suddenly taken ill near the summit of Ben Stack.
He was flown by coastguard helicopter to Raigmore Hospital in Inverness, where he was pronounced dead, said an NHS Highland spokesman.
His wife travelled to the hospital on Sunday afternoon to formally identify the body arriving at about 1300BST (1200GMT) with a police escort and Jim Devine, who was her late husband's election agent.
She spent about 20 minutes at the hospital's mortuary building.
His former wife, Margaret, said their two adult sons were "gutted" by the tragedy and were heading to Scotland.
"He was so young and had so much to offer," she said. "In these troubled political times he was a heavyweight on the right side, not least on the war in Iraq."
Mr Cook's death means there will be a by-election in Livingston, where Mr Cook was MP.
He entered Parliament in 1974 and was a key figure when Labour was in opposition, mounting a damaging attack on John Major's government during the Arms to Iraq affair.
He served as foreign secretary from 1997 to 2001, when he was demoted to leader of the Commons, where he steered a modernisation process.
In 2003, he resigned from the Cabinet on the eve of the Iraq war, arguing that military action was unnecessary.
After his death, Mr Blair said: "This news will be received with immense sadness, not just in Britain but in many parts of the world.
"Robin was an outstanding, extraordinary talent - brilliant, incisive in debate, of incredible skill and persuasive power."
Foreign Secretary Jack Straw called Mr Cook "the greatest Parliamentarian of his generation" and added: "I deeply mourn his loss."
Chancellor Gordon Brown said: "I admired and valued Robin as a colleague and friend and as one of the greatest parliamentarians of our time.
"His wife Gaynor and his two sons are in our thoughts and prayers."
Former Labour leader Neil Kinnock predicted that Mr Cook would have returned to Labour's front bench had he lived.
And Work and Pensions Secretary David Blunkett said Mr Cook should be remembered for major achievements, including protecting people from genocide in Sierra Leone.
UN Secretary General Kofi Annan also paid tribute to the former foreign secretary as a "partner on a wide range of issues".
"Throughout a rich and varied life, Mr Cook displayed exceptional intellect, eloquence, vision and passion in the domestic and international arenas alike," a spokesman for Mr Annan said.
US Secretary of State Condoleezza Rice paid tribute to a "passionate defender of human freedom and dignity."
She said: "As foreign secretary, he played a key role in ending ethnic cleansing and building peace, stability and democracy in the Balkans. We mourn his passing."
Michael Howard said: "Robin Cook's contribution to British politics was immense.
"He was a politician of principle who fought hard for the things he believed in. He will be greatly missed."
And Mr Kennedy said: "Scottish, British and international politics have lost a good and gifted man."
Lord Robertson, a former Nato secretary general and UK defence secretary who enjoyed a 40-year friendship with Mr Cook, said he was "a formidable politician who firmly stamped his identity on British politics".
Sir Malcolm Rifkind, Mr Cook's Tory predecessor as foreign secretary, said his "political strength" had come from his "ability to represent what many might see as a more true reflection of the Labour party than Tony Blair's".
Sir Iqbal Sacranie, secretary general of the Muslim Council of Britain, said Mr Cook's loss would be felt deeply in the Muslim community, particularly because of his opposition to the war.
Meanwhile, human rights group Amnesty International said Mr Cook would be remembered as a "significant" campaigner.
Mr Cook was called one of the Labour Party's "leading lights"
Derek Simpson, general secretary of union Amicus, said: "Apart from being extremely intelligent, Robin Cook was very brave and had more integrity than most politicians could ever dream of having."
Horse racing was one of Mr Cook's passions and he spent time as a newspaper tipster.
Channel 4 racing pundit John McCririck said: "He was so intellectually stimulating and your brain came alive when you were with him."