It happens.
My nom de gaure had already been used by an American Football mascot/cheerleader (retired). I don't know his route to the name, but mine is purely a sartorial affectation. Corporate identity. And a website domain name, wot I grabbed rather swiftly.

http://mister.red

I don't use my real name for the same reason I don't use my real birthdate on insignificances like Fakebook. Security.