Cog is the combined robotic form of Fortress Maximus's vehicular drones, Gasket and Grommet. Cog has no independent will of his (its?) own and is completely under Maximus's control. Functioning as both mechanic and warrior, he allows Fortress Maximus to be at other places while in city mode, as well as to interact with more normally-sized beings.
Made from an old Cog/Gasket & Grommet. I replaced arms and legs with a dollar store Optimus prime, shoulder guns came from a Mega scf PVC Thundercracker.
This was more of an upgrade and a darn good one, If I do say so myself ;)