My various avatars for certain holidays etc.; I don't use all of these everywhere:
My main avatar
New Year's (there's a pun here...)
Pi day (pi on my head, eating a piece of pie)
Easter (rabbit ears)
Fourth of July (fireworks)
Halloween (witch's hat)
Christmas (reindeer antlers)
Black cat (Friday the 13th)
For sites that insist on cropping avatars to circles. I made my avatar as a square, so it should display as a square; it's the principle of the matter. (Increase canvas size by 141.4%, center the original)
When I first made my avatar, I'd just gotten GIMP for the first time, so I was sort of messing around with the gradients and textures there. And also meow. And I kind of like pink and my favorite color's purple, though I don't remember if the color was intentional or just happened to be the result of the blending modes and gradients I used.
In 2017 I decided there were a few things I didn't like about my original avatar, so I decided to redo it:
I wasn't happy with the facial proportions and what expression they looked like, so I decided to trace a photograph of an actual cat and then tweak it a bit.
The forums I originally used my avatar for displayed avatars at whatever size they were uploaded as, but some sites I'm using now scale avatars to a fixed size bigger than my actual avatar. My original avatar was a bitmap so couldn't easily be scaled up; my current avatar has an HD version.
The tiledness of the texture is sort of weird (although I otherwise sort of like the texture)
Also the new avatar has a no-background version in case I ever want that (this would have been harder with my old avatar).
Avatars relating to things going on in the specific forum where I had the avatar