Igor

When your sycophantic right-hand man is actually almost always trying to figure out ways to get rid of you, and your lieutenant is a stoic, withdrawn sort, it's nice to have someone that understands you. Igor fulfills this role with aplomb. Tiny, twisted, cheerful and probably at least a little miswired, the little wretch wants nothing more from life than to gobble up whatever scraps Megatron leaves behind, literally as well as figuratively. Megatron has a vague recollection of the head having used to belong to one of his soldiers, but the possibility doesn't interest him enough for him to invest much thought into it.

Fiction
Igor hung around at Megatron's Decepticon refugee camp in Africa, where he was weird and crazy, eating the occasional minerals that Megatron gathered and brought back to him and the hatchlings. He would often be pleased at his master's return from excursions.

He later traveled with Starscream and his master to Washington, D.C., as the latter prepared to launch his invasion with the use of Sentinel Prime and his Space Bridge Pillars. After Megatron destroyed the statue of Abraham Lincoln seated on the Lincoln Memorial, Igor gnawed happily on its disembodied head. Dark of the Moon

Dark of the Moon adaptations
Igor accompanied his master when the Decepticons invaded Chicago. Following the battle's end, he was last seen staring up at the sky, wondering what had become of his master.