By Shaun Ley
BBC Radio 4 presenter
Ken and Boris. If you're in the UK, you almost certainly know who I am referring to and what they have in common.
That is one example of the impact having a Mayor of London has made in the eight years since the job was established.
Ken and Boris - not Tony Blair's first choices for mayor of London
But Ken Livingstone and Boris Johnson were certainly not who Tony Blair had in mind when he was converted to the idea of directly-elected mayors.
I can remember preparing for an interview with Mr Blair when he was giving a speech on the subject early in his premiership.
Who should slip in to see him, but Richard Branson.
He was much closer to Mr Blair's ideal; a successful entrepreneur, unencumbered by the tribalism of party politics.
Instead, the job has been held by two maverick partisans.
Of course, the whole point of devolving power is that central government should not always get its way.
Even Ken Livingstone's initial victory in the first mayoral election in 2000 was a defeat for the government.
In the programme, Inside City Hall for Radio Four, he describes the campaign to stop him becoming mayor as "poisonous".
In a straight fight between Whitehall and City Hall, Whitehall won
And Nick Raynsford, who was minister for London at the time, says he personally would not have countenanced the efforts used to prevent Livingstone becoming the Labour candidate.
The acid of test of the mayoralty, though, is not name recognition or intra-party battles, it is supposed to be about securing more effective government for London.
On that, the jury is still out. The mayor runs few of London's services, so it is hard to judge what impact "strategic plans" for building or the economy have day-to-day.
He is not in charge of schools or hospitals, his power over the police is arms-length; so the biggest service he can be held responsible for is transport.
That was the subject of the mayoralty's first conflict with central government.
Gordon Brown wanted private business to rebuild London Underground, Mayor Livingstone wanted to issue public sector bonds.
In a straight fight between Whitehall and City Hall, Whitehall won.
The mayor fares best when central government needs him. That happened with the congestion charge.
Nick Raynsford told me it was "inconceivable" that it would have been introduced otherwise. Similarly, ministers need the mayor if the 2012 Olympics are to be a success.
There are signs, though, that the relationship may be changing.
The home secretary Jacqui Smith has accused Mayor Johnson of being irresponsible, for telling Metropolitan Police Commissioner Sir Iain Blair he did not have confidence in him.
Sir Ian resigned. The mayor could not sack him, but it is a sign of the importance of the job that the commissioner felt unable to continue without his support.
Ken Livingstone says that after a while in the job, he realised that it had huge potential, well beyond the powers the legislation prescribed.
Boris Johnson seems keen to put that to the test. The mayor of London is flexing his muscles.
Inside City Hall will be broadcast on Thursday 8 January at 2000 GMT on BBC Radio 4.