Micromaster Overload, that is.
I had a headless 2-pack Optimus figure and was flipping through the MTMTE guidebook for ideas when I came across this little dude. http://tfwiki.net/wiki/Overload_%28G1%29
A simple repaint with the smoke stacks removed to set him apart from Optimus.
The head is a robot heroes Ultra Magnus! Fits perfectly in the roof cavity.
http://i44.tinypic.com/30tlaq0.jpg
http://i42.tinypic.com/mk9geo.jpg
http://i40.tinypic.com/2k31c1.jpg