Although he rose to the second-highest political post in Britain as Margaret Thatcher's deputy prime minister, William - later Lord - Whitelaw will probably be best remembered as the man who took over the running of Northern Ireland at its most violent and chaotic time.
That was in March 1972 following the prorogation of Stormont, and this made him particularly unpopular among unionists. However, in Brian Faulkner's words, the big Cumberland gentleman farmer was "a genial and humane man, deeply affected by the sufferings of others, but possessing the necessary sense of humour to allow him to survive in Northern Ireland."
This made him difficult to dislike, and his warmth and affability allowed him build bridges to Northern politicians of all persuasions. Dr Garret FitzGerald recalls being impressed by his "openness and bonhomie". However, political commentator James Downey noted that "within the teddy bear lurks a man of steel - clever, delicate and sometimes ruthless."
Three months after his appointment he even tried to talk to the Provisional IRA, the only Northern Ireland Secretary to have done so. He met IRA leaders secretly in London, but their demands, notably a British withdrawal by 1975, were too unrealistic to be taken seriously. He later admitted the initiative had been a mistake, although at the time it was believed to be part of a British policy to show that everything had been tried so that the IRA would be seen to be wedded to violence.
Around the same time, he made what he later said was one of his worst mistakes: agreeing to special privileges for paramilitary prisoners, a system which, when the British later tried to remove it, led to the 1981 Maze Prison hunger strike.
In October 1972 he produced a Green Paper - although the title was avoided because of unionist sensibilities - in which the phrase "the Irish Dimension" made its first appearance. This led the following March to a White Paper, which has become the model for the governance of Northern Ireland since. It foresaw a 78-member assembly elected by PR, and power-sharing between the parties as an alternative to unionist majority rule.
In the autumn of 1973 Mr Whitelaw patiently piloted through seven weeks of talks, which often came close to breakdown, but which finally saw the Ulster Unionists, the SDLP and Alliance coming together in a power-sharing executive. Amazingly, just before that December's Sunningdale conference, which was to put the final seal on the agreement and set up the cross-Border Council of Ireland, he was pulled back from Belfast by the then prime minister, Edward Heath, to become employment secretary.
He argued against the holding of the February 1974 Westminster election, in which the crushing defeat of Faulkner's moderate unionists led directly to the debacle of the Ulster Workers strike.
When he retired from the British government in 1988, he said the collapse of the power-sharing executive in May 1974 had been "one of the great sadnesses of my life". In 1992 he described the Northern Ireland post as the most "challenging" of his career and the setting-up of the executive as his "single most successful action".
In the Conservative leadership poll of 1975, Mr Whitelaw stepped in after Mr Heath had resigned after the first ballot, as the representative of "one nation" Toryism, but was soundly defeated by Margaret Thatcher.
Although he disliked Mrs Thatcher's monetarist policies, he put the party first, and supported her until his retirement. He deplored increases in unemployment and did not share her passionate antagonism towards trade unions.
As home secretary in the early 1980s, he came under fire from the pro-capital punishment and anti-immigration lobbies. He told the House of Commons several times that his experience in Northern Ireland had converted him from favouring to opposing the death penalty.
It was on capital punishment that he clashed most publicly with Margaret Thatcher, rounding on her after she applauded pro-hanging delegates attacking him at a party conference to tell her that because of his loyalty, he deserved some loyalty from her.
His viscountcy in 1983 was the first hereditary peerage awarded for nearly 20 years. He presided for five years as Leader of the House of Lords before his retirement on health grounds.