Skull

One of the Destron Headmasters - the most gluttonous, violent and least intelligent of the bunch, often bossed around by the rest. His Transtector takes on the form of a robot crocodile. Note: In Japan, Skull is a small robot who transforms into a head and controls a larger, lifeless Transtector body. The Headmasters toyline referred to the small robot as Grax, with "Skull" being the name of the combined small robot/transtector form, but this distinction of nomenclature is made in fiction only very rarely, with the character usually being referred to as "Skull" regardless of what form he takes. (Source: TFwiki, edited)