He is an outspoken anti-establishment figure known in Britain for introducing congestion charging to free up London's traffic clogged streets.
Mr Livingstone has been London mayor since May 2000
Ken Livingstone has never been afraid of controversy - whether it involves infuriating prime ministers (by going it alone in London) or upsetting pigeon lovers (by declaring war on their occupancy of Trafalgar Square).
His suspension from office on full pay for four weeks for comparing a Jewish journalist to a Nazi concentration camp guard is the latest high-profile episode in his career.
The Mayor has reacted against this latest setback, saying his temporary removal from office is anti-democratic.
His protest and persuasion powers have worked before. In January 2004, he won over National Executive Committee members, and returned to the Labour fold.
Making of a mayor
1969: Joins Labour Party
1971: Elected to Lambeth borough council
1973: Elected to Greater London Council
1979: Fights and loses Hampstead at general election
1981: Elected GLC leader
1986: GLC abolished
1987: Elected MP for Brent East
September 1997: Beats Peter Mandelson to a seat on Labour's NEC
November 1999: Announces bid to become Labour's candidate for London mayor
February 2000: Loses mayoral selection battle to Frank Dobson
6 March 2000: Announces independent bid for mayor
4 May 2000: Elected London mayor
September 2002: Labour rejects Livingstone's attempt to rejoin party
January 2004: Livingstone rejoins the party
His application to rejoin Labour caused ruptures in the party, with Tony Blair apparently privately in favour of the move, while ex-leader Neil Kinnock said he was "fundamentally and irretrievably" opposed.
But an appeal for party unity and assurances of his commitment brought an end to a spell in the Labour wilderness.
The former MP, who in 2002 became a father for the first time at the age of 57, became a public figure in the 1980s as leader of the Greater London Council (GLC).
His reign as GLC leader from 1981 to 1986 coincided with the worst of Labour's wilderness years.
Some of his policies made him a tabloid hate figure; the Sun newspaper once described him as "the most odious man in Britain."
He was in favour of talking to Sinn Fein and the IRA. He was a strong supporter of the recognition of gay rights and measures to address inequality faced by women and ethnic minorities.
His time at the GLC also saw him campaign against its abolition and in favour of its "Fares Fair" policy, which pioneered the use of modern advertising techniques in political communication some time before the wider Labour Party discovered their effective use.
All the while, his wit and apparent calm in the face of unrelenting press attack infuriated his political opponents and made him a popular rebel with Labour's rank and file - and many Londoners.
Mr Livingstone was born in Streatham, south London, on 17 June 1945. He attended Tulse Hill Comprehensive.
He worked as a cancer research laboratory technician at the Royal Marsden Hospital as his political career developed.
In 1971, while training as a teacher and having joined Labour two years earlier, he was elected to Lambeth Borough Council.
In 1978 he opted to fight a seat on Camden Council. He had also been elected a Greater London councillor
Mr Livingstone's first attempt to become an MP failed when he lost in Hampstead at the 1979 general election.
But in May 1981, the day after Labour won a small majority on the GLC, group leader Andrew McIntosh was ousted and Mr Livingstone voted into his place instead.
With Labour in opposition in Parliament, controversies involving the GLC provided a rallying point for party members across the country.
As leader, Mr Livingstone had control of a multi-billion pound budget and real power to wield.
But after the Conservatives axed the council in 1986 and he crossed the Thames from County Hall to the House of Commons as MP for Brent East in 1987, he faced the relative powerlessness of the backbenches.
What's more, by that time Labour's leadership viewed him as an unhelpful nuisance. Neil Kinnock detested him.
He got on better with John Smith, but Tony Blair's ascendancy in 1994 heralded another downturn in the MP's job prospects.
Although a favourite with the party grassroots, he was less well liked in the Parliamentary Labour Party where his high profile and unerring ability to hit the headlines were mistrusted.
His new colleagues also blamed Mr Livingstone, as one of the municipal socialists the tabloids and Conservatives identified as a key figure of the "loony left", for Labour's failure to challenge the Thatcher government effectively.
Mr Livingstone is undoubtedly associated with Labour's left but not predictably so. He has, for instance, long been in favour of proportional representation for Westminster seats - a view not shared by many left-wingers.
He is also in favour of signing up to the European single currency, and had argued for one-member-one-vote elections within the party some time before it became a key issue for New Labour modernisers.
Long before he made the break with Labour to run for mayor, he was a dissident whose refusal to toe the party line won his popularity on the streets of London and beyond.
That undoubtedly came into play when Labour came to choose its candidate to be London mayor.
The saga lasted through 1999 and into the following year, the constant factor being the leadership's determination to halt the Livingstone bandwagon.
When the selection contest formally got under way he repeatedly insisted he would not break from the party if he lost.
But when he came second to Frank Dobson in the race, Mr Livingstone - who actually won more votes than his rival and was defeated by a complex electoral college system - decided to split from Labour and stand as an independent.
It was, he said, the hardest decision of his political life, adding that he had decided to stand because of the "principle of London's right to govern itself".
As mayor, his flagship policy has been congestion charging for central London.
And he unsuccessfully battled against the government's public-private partnership plans for the Tube, which he is now responsible for running.
But he also took a high profile in opposing the Iraq war, calling George Bush "the most corrupt American president since Harding in the Twenties".