The Lord Mayor of London (since 2006 Lord Mayor of The City of London) is a position that should not be confused with that of Mayor of London (currently Boris Johnson).
The Lord Mayor's position has been in existence since the year 1189; Henry Fitz-Ailwin de Londonstone (not one of the Welsh ones, I think!) rather greedily occupied the mayorship for 24 terms. These days, the tenureship is for one year only. In those days (and for a long time afterwards) London comprised what we now know as The Square Mile, ie: the financial centre of The City. What we think of as London these days was a series of small villages outside London proper. Very possibly, even the non-Brits amongst us will have heard of Dick Whittington who was mayor 4 times (and, to his credit, introduced public loos to the populace).
On Friday, The Silent Ceremony takes place with the current mayor handing over his insignia to the new mayor. On Saturday morning, the Lord Mayor's Show takes place ( www.lordmayorsshow.org ) with great ceremony, floats, and all kinds of fun going on. The mayor will ride in his magnificent 18th century coach to take the oath of allegiance. It really is a wonderful show; one year I was invited to watch it from an upper window on Ludgate Hill and it was a marvellous sight. There are usually fireworks in the evening but apparently it's thought that there have been so many fireworks this year with the various celebrations and the Games that they've decided not to do it.
The Mayor of The City of London is one of the most important people in the country, after HM the Queen and the Prime Minister; it's his job to promote London as a financial centre on the world stage. On a daily basis, he's a member of the City Corporation which looks after the city in the same ways as a local council does.
There have been 8 Welsh Mayors, according to the information I've read, the last being Sir David Lewis (2007-2008) who is the grandson of a sheep farmer in the Cothi valley, Carmarthenshire. He has since moved back to Wales. I haven't been able to ascertain which of the others were Welsh as yet but it will be interesting to see when the first one was, given the enmity between Wales and England over the centuries.
updated by @gaynor-madoc-leonard: 11/11/15 10:38:30PM