Mouthplate

Optimus Prime's mouthplate.

Instead of regular human facial features, some Transformers have what looks like a plate affixed to their lower jaw, usually covering up to their nose. While no official name exists for these, they are usually called 'mouthplates ' or 'faceplates ' (despite a 'regular' face once being described as a faceplate in the TV series). Two of the most famous examples are those of Generation One's Soundwave and Optimus Prime.

In earlier series, a Transformer's mouthplate moved when they spoke, as if there were a working jaw underneath. In Robots in Disguise and the Unicron Trilogy, however, it remains static.

Trivia

• Fan commentator Zobovor nicknamed these distinctive items "woobers" (crediting the term to a younger relative), and the name became popular with some fans.

• Both the Armada Optimus Prime and the 20th Anniversary Optimus Prime toys have mouthplates that can move up and down when a button located on their heads is depressed. Additionally, the 20th Anniversary toy has teeth hidden behind the mouthplate, in reference to Optimus Prime's battle-damaged appearance in the Generation 2 comics, though this detail cannot be seen without disassembling the entire head.

• The Cybertron Optimus Prime toy features a mouthplate that slides up to cover his actual mouth when he is to be transformed into Super mode.
  
  
  From Teletraan I: The Transformers Wiki, a Wikia wiki.