Tony Benn was one of the few British politicians who became more left-wing after having actually served in government.
He became the authentic voice of the radical left with the press coining the term Bennite to describe the policies espoused by those resisting attempts to move the Labour Party to the middle ground.
As such, he became a bogeyman for the right in British politics, with delegates to Conservative conferences displaying Ban the Benn badges in the style of CND's Ban the Bomb logo.
Later in life, the former firebrand politician became something of a folk hero as well as a campaigner for a number of causes, particularly opposition to UK military involvement in Iraq and Afghanistan.
Anthony Neil Wedgwood Benn was born in London on 3 April 1925 into a family steeped in radical politics.
Both his grandfather and father had served as Liberal MPs, although his father crossed the floor of the House to join the Labour Party in 1927. He was created Viscount Stansgate in 1942 and sat in the Lords as an hereditary peer.
Benn's mother, born Margaret Holmes, was a leading feminist and an early campaigner for the right of women to be ordained as priests.
His father's political activities brought the young Benn into contact with some of the leading figures of the day, including David Lloyd George and Mahatma Gandhi.
Benn attended the exclusive Westminster School, something he tried to hide in future biographies, and then had a spell as a fighter pilot in the RAF.
He went on to read philosophy, politics and economics at Oxford where he became president of the Oxford Union.
While there, he met his American wife, Caroline, proposing to her after a whirlwind nine-day courtship.
Benn spent a brief spell as a producer with the BBC before being selected to fight Bristol South East after the incumbent, Sir Stafford Cripps, had resigned due to ill health.
Benn won the subsequent by-election, entering Parliament on 4 December 1950 as the youngest MP in the chamber. His political views during the following two decades would remain centre-left.
"I'm on the right wing of the middle of the road with a strong radical bias," he once said.
But his future in politics was in doubt. The death of his elder brother Michael during the war meant he would eventually succeed to his father's title.
Hereditary peers were barred from sitting as members of the House of Commons, but his attempts to remove himself from the succession failed.
The death of his father in 1960 precipitated a crisis. Still insisting on his right to abandon his unwelcome peerage, Tony Benn fought to retain his seat in the by-election on 4 May 1961, caused by his succession.
Sinking the pirates
Although disqualified from taking his seat, the people of Bristol South East still re-elected him as their MP.
But a subsequent election court gave the seat to the Conservative runner-up, Malcolm St Clair.
Outside Parliament, Benn continued his campaign, and eventually the Conservative government accepted the need for a change in the law.
The Peerage Act 1963, allowing renunciation of peerages, became law on 31 July 1963 and just 22 minutes later he became the first peer to renounce his title.
His Conservative opponent in Bristol immediately resigned the seat and Benn swept back into the Commons following a by-election in 1963.
When Labour returned to power in 1964, Benn was appointed postmaster-general. In that role he oversaw the opening of the Post Office Tower (now the BT Tower) and introduced Girobank.
However, his proposal to remove the portrait of the Queen from postage stamps was firmly rejected.
Benn also introduced the legislation that closed down the pirate radio stations which had sprung up around the coast of Britain.
The Marine Broadcasting Offences Act made it almost impossible for operators such as Radio Caroline to continue transmitting offshore and paved the way for the BBC to launch Radio 1.
In 1967, he became minister of technology with responsibility for the development of Concorde.
With Ted Heath's Conservatives winning the 1970 general election, Benn turned his attention to campaigning for a referendum on Heath's plans to take Britain into the European Economic Community.
He remained a fervent opponent of European integration, claiming that Europe was bureaucratic, centralised and dominated by Germany.
In 1975 he campaigned for a No vote when Harold Wilson's Labour government finally allowed a public vote on the issue.
As Wilson's secretary of state for energy, Benn encouraged a number of workers' co-operatives in a bid to keep struggling firms afloat.
The most notable was Meriden in the Midlands, which continued to produce Triumph motorcycles for another decade.
He also stood for leadership of the Labour Party when Wilson resigned in 1976. He lost on the first ballot and switched his support to Michael Foot, who subsequently lost out to James Callaghan.
His decision to support Foot was a mark of his shift to the left, which he later attributed to his experience as a cabinet minister.
He said he had come to the conclusion that Britain was ruled by vested interests and that elected MPs wielded little power.
"If the British people were ever to ask themselves what power they truly enjoyed under our political system they would be amazed to discover how little it is, and some new Chartist agitation might be born and might quickly gather momentum."
By now he had dropped Anthony Wedgwood Benn in favour of the more populist Tony Benn.
His policies endeared him to the left of his party where he became a conference favourite.
He campaigned for conference decisions to become binding on the party.
He insisted an incoming Labour government should embark on a massive process of nationalisation, remove controls on trades unions, withdraw from the EEC and abolish the House of Lords.
The latter institution he once described as "the British Outer Mongolia for retired politicians".
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
Despite his popularity with the rank and file, he failed to beat Denis Healey in a contest for the deputy leadership of the party and his decision to stand saw a split on the left.
His support for Sinn Fein and a united Ireland, together with his opposition to the British military action in the Falkland Islands, made him a target for the popular press.
In 1983, boundary changes saw his Bristol South East seat disappear and, in what was seen as a shock result, he lost the new seat of Bristol East to the Conservatives.
However, he was not out of Parliament for long and won Chesterfield in a by-election in 1984.
During the miners' strike of 1984-85, he was a strong supporter of the NUM president, Arthur Scargill.
After the return to work he attempted, unsuccessfully, to introduce a bill in the Commons giving an amnesty to all miners imprisoned for offences during the strike.
After Labour's third successive election defeat in 1987, he stood for the leadership against Neil Kinnock but was heavily defeated.
His party was now moving away from his views in an attempt to reclaim the middle ground of British politics. Benn was becoming unfashionable.
He finally stood down from Parliament before the 2001 election in order, as he put it, "to spend more time on politics", and threw himself into campaigning against the Iraq war, becoming president of the Stop the War Coalition.
He seemed to mellow in his later years and became a regular pundit on radio and television as well as occasionally appearing on stage with folk singer Roy Bailey.
He was also a compulsive keeper of diaries, both in written form and on audiotape; extracts from the latter have appeared on BBC Radio.
In 2006, he topped a poll commissioned by the BBC's Daily Politics programme to find who people considered to be their political hero, beating Margaret Thatcher into second place.
Subject as he often was to personal attacks from his opponents, Tony Benn held to his view that politics should be about policies and not personalities.
"This idea that politics is all about charisma and spin is rubbish," he said. " It is trust that matters."