Good question. I have often mulled about this over many sleepless nights.
It was an alias. He was actually an Irishman called Paddy O' Driscoll. He changed his name so that he could break into the Italian renaissance art movement., which was a bit cliquish in those days.
He did a very clever thing and stuck the " O " from " O'Driscoll " on to his alias Leonard. The rest is history.
And who on earth would buy the Mona Lisa with a name like Paddy O'Driscoll? Hope this helps.
In Dublin there's a well known art supplies shop called O'Driscolls, selling all sorts of things, including oil paints which is what DaVinci used to paint Mona.
Also, just round the corner is a Masonic Lodge, so, putting all the clues together, it is difficult not to jump to the conclusion that O'Driscolls art supplies is, in fact, the final resting place of the Holy Grail.
Actually he was "Leonardo di ser Piero da Vinci", meaning "Leonardo, son of (Mes)ser Piero from Vinci."
I think the origin of the name with the O on the end might mean 'son of' Leonard, although that could be mde up - and in any event LdaV was illegitimate.
There is also a famous actor called Leonard DiCapri named after a very popular car made by the Ford Motor Company.