Over the course of the first two G.I Joe films - G.I. Joe: Rise of Cobra and G.I. Joe: Retaliation - 29 of the classic comic book characters have been brought to life (and death) in the form of either leading roles, un-credited background appearances or fleeting cameos. However, there are well over 100 characters in the G.I. Joe universe for writers of the next installment to choose from.
Some characters have very little back story to draw from, so they wouldn't work well on film - but others are ripe for adaptation.