Character model
A Character model refers to a character's in-fiction appearance (as opposed to their toy).
Character models can be radically different from their toy (example: Ratchet).
Sometimes the same toy used for two characters can be understood to have radically different in-fiction appearances, as in the case of Sideswipe and Red Alert . (see illustration at right) These two toys are essentialy identical, but while the first design conceived - Sideswipe's - is tall and athletic, the second - Red Alert's - is short and stocky, a general rule that applies to second-season characters that shared toy molds with first-season characters (Trailbreaker/Hoist, Prowl/Smokescreen, the Seekers/the Coneheads). Despite being based on the same toy, they do not "look" the same, though it is generally held that the stockier second season designs bear closer resemblence to the toys themselves.
Hot Rod is notable for having two different character models based on the exact same toy, mold, colors, etc. The 1986 toy represents his lithe form in Transformers: The Movie. That same toy also represents his smaller, bulkier form as "Rodimus Major" in the Beast Machines era.
