I had an unwanted alter ego once. A colleague called me by the wrong name for the entire time we worked together (a few months). I considered correcting him, but I wanted to see how it would play out.
if you didn't correct him, then it wasn't unwanted. so how did it play out?
It was initially unwanted, but it became interesting because it lasted so long. What made it possible was that we didn't work closely (different groups) and encountered each other only infrequently and usually one-on-one, so there weren't others around to correct him. When I left, there was a social event with mainly people from my group, so he was not present, and I don't actually know whether he ever learned of his error. Maybe my alter ego still lives in his memory.