Heh, I had originally always gone by the online moniker of "KingofAnime" ever since I first started crawling on the internet. It was a combination of my last name, (I make an unholy amount of puns based on my last name irl) and obviously anime. In my defense, I was in 5th grade and was really into it at the time!
Anywho, I've always been known as this no matter what site I went to. As it came to pass, I began to despise anime deeply and just ceased to watch it anymore. However, seeing how I haven't been known as anything else online, I kept the name out of respect for what it meant to me and because I grew attached to the name itself. The online communities just started calling me KoA as a shortened nickname and because it sounds cooler and more enigmatic.
When I first signed up to Smogon, I was "KingofAnime-KoA"; still retaining my old moniker, but warming over to KoA. As I began to be assimilated into Smogon and the users started referring to me as just KoA, I felt it was ok to let go and decided to permanently become just KoA.
Now the past few forums I have joined, I register simply as KoA. No one needs to know of the ancient love I had for a rather annoying style of animation. It was only just recently that I ditched the unabridged form of my online alias on Shoddy and go by KoA there as well.