The Mayor. Thouigh it must be pointed out that, in most places in the UK, the Mayor is simply the Chairman of the local council, is not directly elected, has no power and spends most of his time opening things and representing the Borough/Town rather than governing it. Councils have a convenor, with cities calling the convenor the 'Provost'
Ken Livingstone was Mayor of London in 2007. The present Mayor is Boris Johnson.
Mayor Boris Johnson of the conservative party
Sir William Bolton
There is no manner of address for the Mayor of London other than "Mayor."
Sadiq Khan is the first Muslim Mayor of London.
Mayor of London's Sky Ride was created in 2007.
Boris Johnston is Mayor of London.
Despite it's name it is NOT the City Hall for London or even in the City of London. It is the Headquarters of the Greater London Authority which is led by the Mayor of London. (NOT the Lord Mayor of London, who is a member of the much older City of London). The Building is privately owned and so presumably built to the order of the land owner who is currently a property company called 'More London'.
Richard Martin - Lord Mayor of London - died in 1617.
William Rowe - Lord Mayor of London - died in 1593.
In the case of London - "The Rt Hon The Lord Mayor of the City of London"
It depends on the year. For example, in 1594, the Lord Mayor of London was John Spencer.