It's Derpy with a rocket launcher. Does there need to be a description?
Based on a comment where someone wanted to make a background with Derpy here's a 1024x768 version of it with no background (PNG): [link]
Heres a Jpeg version that fits the file size for using it in TF2, in case you want to use it as a spray (I know Jpegs suck, but I had problems getting it to load as a TarGa file, so . . . Sorry.) :[link]
If you're having problems with either of these, let me know.