LDog is the name I play under in a few games (America's Army, Planetside, etc).
It used to be LakenheathDog, but the name was a bit long for most people to remember (let alone quickly type out).
The origin of the name is a bit silly ... when I was in the U.S. Air Force and stationed at RAF Lakenheath in the UK, my nickname was Odie. You know, the lovable dog who is always smiling and doing stupid things ...
Anyway, that's the origin of the name and now I'm kind of stuck with/on it.