Ken Livingstone is the rebel who became part of the establishment.
In the 1980s, during his first reign over London, he was a left-wing firebrand who was almost as much of a thorn in the side of Labour's leadership as he was for Margaret Thatcher. Two decades later, he defied Tony Blair's New Labour to win the newly-created position of London mayor.
But now he is in new political territory, no longer the maverick but the party's official candidate for the second time running, with Gordon Brown among those joining him on the campaign trail.
Kenneth Robert Livingstone, 62, was born in Lambeth, south London, at the end of the Second World War.
He went to Tulse Hill Comprehensive School before training as a teacher, then becoming a technician for a cancer research institute. He joined the Labour Party in 1969 and went on to become a Labour councillor in Lambeth.
He led the Greater London Council during the turbulent years of the early 1980s, famously goading Mrs Thatcher across the Thames in Parliament by hanging a banner from County Hall with the unemployment figure on it.
At the GLC, 'Red Ken' became a bete noire of the right, supporting everyone from striking miners to Sinn Fein's leaders at the height of the IRA's bombing campaign. After the Tories abolished the GLC in 1986, Mr Livingstone crossed the Thames, becoming MP for Brent East a year later.
At Westminster, he joined the ranks of Labour's left wing MPs, harrying the Tories but also clashing frequently with his own party's modernisers.
He had a fraught relationship with the New Labour leadership and was expelled from the party for standing for Mayor as an independent in 2000 after Tony Blair opposed his candidature.
Relations slowly improved as he established himself as Mayor and he was gradually welcomed back to the Labour fold. Mr Livingstone is running for a third term on his record.