Former cabinet minister and veteran left-wing campaigner Tony Benn has died at home, his family has said.
The 88-year-old former Labour MP had been seriously ill.
Mr Benn became an MP in November 1950 and served in the cabinet under Harold Wilson and James Callaghan.
A major figure on the left of the party, he narrowly missed out on the deputy leadership in 1981 and was a popular public speaker, anti-war campaigner and political diarist.
In a statement, his children Stephen, Hilary, Melissa and Joshua said Mr Benn died peacefully early this morning at his home in west London surrounded by his family.
"We will miss above all his love which has sustained us throughout our lives," the family said.
"But we are comforted by the memory of his long, full and inspiring life and so proud of his devotion to helping others as he sought to change the world for the better."
They said arrangements for his funeral would be announced in due course.
'He treated me as an equal'
Aged just 25 when he first entered Parliament, Mr Benn subsequently renounced his peerage, which he inherited on his father's death, to remain in the House of Commons.
He served as an MP for more than 50 years, becoming secretary of state for industry in 1974 under Harold Wilson and going on to become secretary of state for energy, keeping his post when James Callaghan became PM in 1976.
But after the Labour government was ousted in 1979, he staged a bitterly divisive battle as the champion of the left with Denis Healey for the deputy leadership of the party.
He retired from Parliament in 2001, famously saying he wanted to "spend more time on politics".
A prolific writer, the last of his nine volumes of diaries was published in October.
Labour leader Ed Miliband led the tributes to an "iconic figure of our age".
"He will be remembered as a champion of the powerless, a great parliamentarian and a conviction politician," he said.
"Tony Benn spoke his mind and spoke up for his values. Whether you agreed with him or disagreed with him, everyone knew where he stood and what he stood for."
Mr Miliband revealed he paid a visit to Mr Benn in hospital recently, describing him as being "as sharp as ever in mind".
He said: "As I left he said to me 'Well, old son. Let's have a proper talk when you have more time'."
He added: "He believed in movements and mobilised people behind him for the causes he cared about, often unfashionable ones. In a world of politics that is often too small, he thought big about our country and our world.
"Above all, as I had cause to know, he was an incredibly kind man. I did work experience with him at the age of 16. I may have been just a teenager but he treated me as an equal.
"It was the nature of the man and the principle of his politics."
Prime Minister David Cameron said Mr Benn was "a magnificent writer, speaker, diarist and campaigner, with a strong record of public and political service".
"There was never a dull moment listening to him, even when you disagreed with everything he said."
Former Labour Prime Minister Tony Blair said: "Tony Benn was one of those rare things: a genuine radical for all his life. He was a fearless campaigner and a legendary figure for the Labour movement.
"Even when I disagreed with him, I always had enormous respect for his brilliance, his passion and his commitment to the people of Britain and of the world."
Ex-Labour PM Gordon Brown also paid tribute to a "powerful, fearless, relentless advocate for social justice and people's rights".
He said Mr Benn's speeches will continue to have a "profound influence on generations to come".
But Joe Haines, who was chief press secretary to Harold Wilson in the 1970s, gave a more critical assessment of Mr Benn's political legacy.
"He did one great thing in his life: he changed the constitution of the House of Lords.
"Apart from that he symbolised the sort of left-wing nuttiness that nearly destroyed the Labour party in the late 1970s and early 1980s."
In a recent interview for Radio 4's Today programme, presenter James Naughtie asked Mr Benn to summarise where he had been "most right" and "most wrong" in his career.
"I made every mistake in the book," Mr Benn replied. "But making mistakes is how you learn.
"I would be ashamed if I ever said anything I didn't believe in, to get on personally.
"You look back and, when you're in a critical mood, you see you made errors of judgement. But as long as you say what you believe and believe what you say - that's the test of authenticity."