But he was fated to spend more than two-thirds of his career in opposition, and only briefly achieved cabinet rank.

A moderniser before the term was invented, he vigorously opposed Labour's shift to the left after Margaret Thatcher's victory in 1979.

As Neil Kinnock's deputy leader in the 1980s, he encouraged his party to embrace multilateral disarmament, the market economy and the European Union.

As a result, they saw off the challenge of the SDP and laid the foundations for New Labour which, eventually, resulted in the 1997 Blair landslide.

Roy Sydney George Hattersley was born in Sheffield on 28 December 1932, into a family steeped in Labour history.

His mother, Enid, who served a term as the city's Lord Mayor, described herself as being born into the party.

His father, also called Roy, shared her political drive. He had once been a Catholic priest - before quitting the church to run off with Enid, two weeks after he'd married her to someone else.

Young Roy was a political campaigner in his early teens, delivering leaflets and knocking on doors in support of local councillors and parliamentary candidates.

He won a scholarship to Sheffield Grammar School before going to the University of Hull to read economics, following a friend's suggestion that it was an essential subject for any budding politician.

On leaving Hull, he worked briefly in a Sheffield steel mill and spent two years teaching in further education.

In 1956, he was elected to Sheffield City Council, and served, for a time, as chairman of the housing committee.

But his political ambitions lay at Westminster.

In 1959, he fought the seat of Sutton Coldfield, failing to dislodge the sitting Conservative MP as Harold Macmillan won a landslide nationally.

And over the next three years, Hattersley unsuccessfully applied for 25 seats before being selected for the Conservative marginal of Birmingham Sparkbrook.

In the general election of October 1964, Hattersley won the seat as Labour scraped back into power with a parliamentary majority of just four.

His career got off to a slow start.

This was partly due to his previous support for the former Labour leader Hugh Gaitskell, who was an opponent of unilateral disarmament and other policies sacred to the Trade Unions.

As a result, Harold Wilson kept Hattersley at arms length.

He got his first foot on the ladder when he was appointed parliamentary private secretary to pensions minister Margaret Herbison. But it was three years before he received his first ministerial posting.

In 1968, Roy Jenkins and Tony Crosland urged Wilson to promote him, and he became an under-secretary of state at the Ministry of Labour, under the forthright Barbara Castle.

His first task was to help implement the unpopular Prices & Incomes Act, which sought to hold down wages to curb inflation.

At the same time, Castle was trying to roll back the power of the Trade Unions.

She outlined her proposals in a White Paper, In Place of Strife. Amongst other measures, it suggested a ballot was needed before strike action was taken.

There was a bruising row in Cabinet and Castle's plans collapsed, and Hattersley moved to the Ministry of Defence.

In 1969, he was required to sign the order that sent British troops into Northern Ireland - while his boss, Denis Healey, recovered from a trip to hospital.

Hattersley also disbanded the B Specials, the controversial reserve police force, replacing it with the Ulster Defence Regiment.

In the 1970 general election, he held his seat but Labour was out of office and he spent all but five of the next 27 years in opposition.

Hattersley was appointed shadow spokesman on foreign affairs, and became a keen supporter of the Common Market.

And he was one of 69 Labour MPs who voted, with the Conservative government, in favour of British entry - an issue that would split the Labour Party for the next two decades.

When Labour regained power in 1974, Hattersley was made minister of state for foreign affairs.

His primary task was the renegotiation of the terms of British membership of the EEC - the organisation that later became the European Union.

In 1976, he supported Jim Callaghan in the leadership election, and was appointed secretary of state for prices and consumer protection - his final Cabinet post.

But three years later, Labour was swept out of office following the industrial strife of the Winter of Discontent, and the Conservatives held power for the next 18 years.

Hattersley became shadow minister for the environment and helped organise Denis Healey's unsuccessful leadership campaign.

But Labour was ideologically split down the middle, and it was the candidate of the left, Michael Foot, who won.

Hattersley was appointed shadow home secretary.

Despite believing that the Labour left was leading the party to oblivion, he refused join many of his political soulmates, who had left to form the centrist SDP.

In 1983, Labour stood on a leftwing manifesto and was soundly defeated.

In the aftermath, Hattersley stood for the leadership but was defeated by Neil Kinnock - and settled for the post of deputy leader.

Together, the so-called "dream ticket" worked to eradicate Militant - a Trotskyite far-left group - in the hope of making Labour electable again.

This meant throwing out policies previously seen as party shibboleths, but victory remained elusive.

After two election defeats, both Hattersley and Kinnock resigned.

They had rejected unilateral disarmament, accepted that Britain's future lay in Europe, stopped short of full-throated support of the miners' strike, and spoke warmly about the market economy.

But it had not been enough.

Hattersley supported John Smith in his successful bid for the leadership, but - having turned 65 - left Parliament at the 1997 election.

He was created a life peer, Baron Hattersley of Sparkbrook, and - having done so much to pave the way for New Labour - promptly became one of its most visible critics.

"Blair's Labour party is not the party I joined", he declared and publicly backed Gordon Brown.

But when Brown finally entered No 10, Hattersley continued the offensive claiming that Labour had managed to alienate all sections of society.

"By attempting to be all things to all voters," he wrote, "it seems to have lost both its moral compass and its nerve."

Away from Parliament, Hattersley was a prolific author.

He published a number of autobiographical books, as well as biographies of John Wesley and William and Catherine Booth, the founders of the Salvation Army.

After widespread press coverage of an incident when his dog killed one of the Queen's geese in St James's Park, Hattersley produced Buster's Diaries, purportedly written by the animal itself.

A dedicated supporter of Sheffield Wednesday, he continued to write for newspapers and magazines, and was a frequent political pundit on radio and television - where he was critical of New Labour and Tories alike.

Following his failure to honour a number of commitments to appear on the BBC's topical quiz show, Have I Got News For You, he was once replaced by a tub of lard - something he took in good part when he finally made an appearance.

He took the same relaxed view about his latex puppet in the satirical series, Spitting Image, which mocked his slight speech impediment and sprayed saliva when it spoke.

In 2013, he separated from Molly, his first wife, after 57 years of marriage. Later that year, he married Maggie Pearlstine, his literary agent.

Five years later, he retired from the House of Lords - briefly re-entering the political fray after the Brexit referendum, when he helped campaign for a second vote.

Entering his tenth decade, he remained alert and politically engaged, opining that he thought Sir Kier Starmer would be a "steady" prime minister after the 2024 general election.

Hattersley once joked that Margaret Thatcher changed the political weather, and "it hasn't stopped raining since".

And because of her, he never had the opportunity to serve in one of the great offices of state.

It was hugely frustrating for him not to have been able to implement the policies in which he passionately believed.

And instead, he will be remembered for reforming the Labour party, when many like-minded colleagues left it.