I was Flibber T. Gibbet for a few weeks during some name change frenzy/event/whatever. I probably would have kept it for a few months if someone hadn't changed it back when I wasn't looking. It was a legit name change.
Mandalorian XIII, which was basically fan service to myself because at the time I found that stupid story terribly entertaining. I think it was part of the Elections, too.
Legendary G13, because apparently just plain ol' G13 was too boring for some of the old farts in the staff forum. I think we compromised on that when G13 was shot down for being too short or something, and we pulled out an old PM I sent BoB from when I joined asking if he would change my name to Legendary Guardian XIII (I was once under the misconception that Jecht was a badass and that my internet persona should mirror that for some reason ). The nicknames that came from Legendary G13 focused on the first part of the name rather than the one I had already delivered on a silver platter at the end of the name, and really, who was I kidding, I'm not legendary at all.
So now I'm just G13. I like it. I identify better with it, and I still get to keep my original username in a way. I might go back to Guardian XIII some time in the future, but for now I'm content being an acbronym.