Now that I actually have an avatar, it's gaming related. Well, mostly.
I used to use a standard revenant avatar at most of the forums I visited. But, at a different forum(what used to be my primary political and off-topic discussion forum), there was a tradition of sticking a Santa hat on your avatar around Christmastime. I never changed my avatar back to the non-hatted version one year, and it stuck.
Then someone on a different forum made me this awesome hand-drawn version, and I've stuck with it ever since. Well, after adding a little colour, anyway.