Well, I started out using my initials and such as my online name (well, usually TC or something, because that's my first initial and middle initial), before 2003. After that, I started using video game characters (mostly Final Fantasy characters). I then came up with a unique XBL name, which became my name here originally and a few places. However, due to having a lot of bad luck with that name, I felt it was best to completely ditch it. I started off as "XenoKnight", because I'm strange and Knight is my favorite character class in RPGs. Didn't work out too well either, so I decided to alter my name. I actually knew someone who had an AIM name "TheManaSwordsman" or something, and when trying to think of a new forum name somewhere, I just stuck "The Mana Knight", because I do like Knights, and I do like many RPGs containing Mana (I do like Mana because it's magic), so I pretty much become a Magical Knight.
Over a year ago, I decided to drop "The" from my name when signing up (I would here if there wasn't someone who registered under my name slightly"). ManaKnight is the online name I've stuck to the longest time, and don't really want to change it. If I cannot have it, I have several variations of ManaKnight (most of my AIM friends know that too, lol).