He is a figure who generates so many myths it is hard to separate the legend from reality. He was by no means the only architect of the Labour Party's modernisation. But he has, like Mao's comrades in 1948, a special place in the history of the long march back to electability begun by Neil Kinnock when he became Labour leader in 1983.
Indeed if anyone should take the blame or credit for the rise of Mr Mandelson it is Mr Kinnock, who backed his appointment by the National Executive Committee as director of communications in 1985.
Mr Mandelson proved an invaluable ally to Mr Kinnock, and to the sometimes underappreciated Patricia Hewitt and Charles Clarke, in the then Labour leader's heroic struggle to reverse the huge setbacks to the party's popularity inflicted by the surge of Bennism five year earlier. Ruthless with those he saw as putting obstacles in the leader's way, he made more enemies in this period than many politicians do in a lifetime.
Strange as it seems now, Tony Blair, and to a lesser extent Gordon Brown, were once, at least in one respect, Mandelson proteges. Mr Blair, especially, was "trained up" by Mr Mandelson in the art of handling the media - an important skill for a man who would become the most media conscious of post-war prime ministers. As Mr Mandelson started to see as early as the 1987 election when he had been director of communications, Mr Brown and Mr Blair were not only the most talented politicians of their generation but were also developing a far-reaching vision for how Labour could once again become the natural party of government.
In policy terms he was nowhere near as inventive as either Mr Brown or Mr Blair. But his conviction as a Labour Party revisionist, his expertise in devising a media "line to take" on any particular issue, his ability to compress it into a soundbite that would lodge in the public mind, and his knowledge of which journalists would be most receptive to which message, were all invaluable assets to his more senior colleagues.
From 1988 to 1990 and again from 1992 to 1994 the three men increasingly worked together until they were acting as an almost inseparable trio. The traumatic period of uncertainty over whether Mr Brown or Mr Blair would run after John Smith's death famously sowed the seeds of the enmity between Mr Brown and Mr Mandelson, who became convinced that of his two moderniser friends it was Mr Blair who looked the likely winner.
But while one side of one of the most remarkable triangles in British politics was fractured, the other two - those between Mr Brown and Mr Blair and between Mr Mandelson and Mr Blair - remained intact. Blair regarded him as too controversial a figure within the Labour Party to make him an open member of his leadership campaign team. But as "Bobby" he performed a clandestine and central role, giving his usual mixture of media, tactical and strategic advice. And continued to do so, with Mr Brown, up to the general election. While Mr Brown was in charge of the campaign and its strategy, Mr Mandelson had spent the best part of two years planning its mechanics while continuing, with the Shadow Chancellor, to give a stream of political and, with the help of Philip Gould, polling advice.
It seemed baffling to many in a party which took the best part of a decade to shake off its hostility towards the press that someone whose skills and experience were in media relations should come to assume such importance.
But that overlooks two important points. One is the nature of oppositions, for whom the media, or as Mr Blair himself once put it "hand-to-hand fighting" for the day's headlines, is virtually the only weapon, apart from Parliament, at their disposal. The second, as Mr Mandelson had been one of the first prominent Labour figures to realise, is the truth that in modern politics it is impossible to separate the medium from the message.
Just as the good salesman whose product is thought to be unsafe or useless goes back to his bosses and tells them to change the product, so the political media man begins, for better or worse, to influence policy.
This helps to explain not only Mr Mandelson's role, but the increasing importance of his old friend Alastair Campbell in the Prime Minister's inner counsels. Mr Blair may have needed Mr Mandelson's personal advice less as he grew into the premiership, but Mr Mandelson also gave him, in the notoriously friendless world of high politics, friendship.
Last but not least, he was a lightning conductor. As the leadership's most unpopular figure he was able to do down its enemies and take the heat by being its public defender when it got into trouble. And in all this Mr Mandelson had a revisionist clarity that dated at least from his time as a Lambeth councillor in the early 1980s, engaged in almost nightly internal conflict with the Trotskyite left.
Mr Mandelson has never been short of faults; but inconsistency hasn't been one of them. There will no doubt be jubilation in many quarters of the Labour Party this Christmas. But not much in No 10.Reuse content