Ed Miliband has led tributes to former Labour cabinet minister and veteran left-wing campaigner Tony Benn, calling him an "iconic figure of our age".
Mr Benn, who has died aged 88, was an MP for more than 50 years and served in the cabinet throughout the 1970s.
Mr Miliband said he would be remembered as a "champion of the powerless".
But former Chancellor Denis Healey said the far-left views of his rival for the deputy leadership in 1981 had been "very damaging" for the Labour Party.
A major figure on the left of the party, Mr Benn was a popular public speaker, anti-war campaigner and political diarist.
The Labour leader said Mr Benn, whose son Hilary is a member of Mr Miliband's shadow cabinet, was a great parliamentarian and a conviction politician.
"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."
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 became secretary of state for industry in 1974 under Harold Wilson and went on to become secretary of state for energy, keeping his post when James Callaghan became prime minister 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.
Prime Minister David Cameron, and his predecessors Tony Blair and Gordon Brown, were among those who paid tribute to Mr Benn's campaigning zeal, radicalism and humour.
But Lord Healey said Mr Benn had been "very difficult to work with".
The peer told the BBC: "He was the hero of the left wing in his early years, but of course that type of left-wing Labour Party didn't appeal to the public at all, so he was very damaging to the party."
His "real legacy" was the supersonic Concorde passenger plane, Lord Healey argued, which turned out to be "a great waste of money".
But former London mayor and ex-Labour MP Ken Livingstone said Mr Benn had been "demonised relentlessly" during his career and was not to blame for Labour's 1980s turmoil.
"A chunk of Labour right-wingers defected and that split the Labour vote," he said.
"They were actually broadly lining up behind the Thatcher strategy, as eventually Tony Blair did.
"But here we are: as in America, that Thatcher-Reagan neo-liberal agenda has failed us terribly, and destroyed millions of lives.
"Tony Benn had an alternative. The tragedy for Britain is that he never got to be prime minister and put that alternative into effect."
Former Labour minister and Lib Dem peer Baroness Williams said that, despite his passionately-held views, Mr Benn "didn't let himself turn into a sour partisan like a lot of politics today".
She told the BBC's Daily Politics programme: "If he disagreed, he would lay out his reasons for disagreement."
Respect MP George Galloway, who was expelled from the Labour Party, told the BBC that Mr Benn was a "really quite majestic figure" who had inspired millions of people.
"The point that's being made over and over again is that most people disagreed with Mr Benn but they admired him, and so on.
"But actually on the issues that he stood for, most people agreed with him, then and now, from his attempts to bring oil into public ownership in 1974 as the energy secretary right through to the war on Iraq and attitudes to nuclear weapons and the European Union."
Mr Benn 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.
Joe Haines, who was chief press secretary to Wilson in the 1970s, said: "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."
Tony Benn, 1925-2014
years as an MP
Aged 25 when he became an MP
Renounced his peerage in 1963
Served in 4 ministerial roles
Steve Richards, political columnist for the Independent newspaper, told the BBC that Mr Benn was the most memorable orator in British politics.
"Some of his ideas around democracy and accountability are very fashionable now, and indeed not just in the Labour Party but in the Conservative Party too."
BBC Parliament will broadcast an evening of programmes in memory of Mr Benn from 19:15 GMT on Friday.