Years ago, I was active in the Society for Creative Anachronism (SCA). If you've ever been to a Renaissance festival, you may have seen people in armor whacking each other with rattan swords. That's not the entire SCA, but it's the most visible part.
(If the "swords" were made of foam rubber without a rattan core, or anyone on the battlefield "cast a magic spell" on another participant, then it probably wasn't the SCA, but I digress.)
Anyway, the name I used for my persona, or character, in the SCA was Karl Kellerman. My research suggested that it was a name that could have existed, but it wasn't a specific historical person's name. (Them's the rules - no Gandalf Bagginses or Napoleon Bonapartes allowed.)
I met a couple with a 2 year old daughter, and they introduced me to her as Karl. Weeks later, when we got together to hang out away from the chain mail, tunics and fencing masks, they tried to tell her my name was Bob. She may have been 2 years old, but this little girl already knew when adults were passing off ridiculous lies. I was Karl, and she knew it. She was having none of this "Bob" business.
Eventually, as a compromise, her parents began referring to me as KarlBob. That was acceptable, even to infallible 2-year-old logic. Other members of our local SCA group heard the new name, and it stuck... and spread. There were people in the group who not only knew me as KarlBob, they had never heard me called Karl or Bob without the other name. The name stuck so well that I still use it on message boards to this day.