RG-4 is a robot who was brought onto the Scar City Butterflies after his predecessor, RG-3, was shut down after a tragic accident.
RG-4 has no concept of humour and strive to try and understand it.
"RG-4 does not undertsand the appeal of a banana hitting a fellow human being in the face," -- Episode 28His outer shell is made of Volcaneic Ash.
RG-4 has a specialised 'Oil Boy' robot who tops him up when he's running low on fuel.
First introduced: Episode 27