- Guiltar is a Quintesson creation from the Generation 1 continuity family.
One shall stand, one shall...um...I guess also stand.
Guiltar, also known as the "Great-Gun Soldier", is a bizarre, vicious fusion of Optimus Prime and Megatron, sent to attack both Autobot and Decepticon alike. It is ultimately a lifeless shell created by the Quintessons, animated by the "ghost" spark of Starscream.
It has a massive artillery truck mode, as well as multiple gun configurations for its robot mode. Physically, it can hold its own against many of the toughest Transformers.
- (Note: The Romanization of the character's name given here is not "official"; there isn't one. There are any number of ways to spell it from the katakana given, including but not limited to Guiltall, Guilthol, Guiltole, Guiltoll, and Steve. This is just the simplest one that seems "right".)
Fiction
The Transformer manga
It's a better truck mode than THS Convoy, at least
Guiltar rose from the sea off of Japan, seeking out Rodimus Prime, who was engaged in a one-on-one battle with Galvatron. Just as Rodimus appeared to gain a decisive victory over his enemy, Guiltar attacked Rodimus from behind with a variety of artillery modes, sending the Autobot leader flying. As it turned out, the one-on-one showdown Galvatron had invited Rodimus Prime to was in reality a trap.
Galvatron revealed that Guiltar was a Transformer created by the Quintessons, who had risen up the ranks of the Decepticons... because apparently, Galvatron doesn't have any accumulated memory whatsoever. As Galvatron gloated over his fallen enemy, and praising Guiltar's obedience, Guiltar snuck behind him and attacked, savagely beating Galvatron and kicking him to where Rodimus had fallen. Revealing his true intentions, Guiltar was gunning for leadership of the Decepticons, which even a concussed box turtle could have seen coming. But not Galvatron.
Preparing to complete the preparation for completion.
Down, Galvatron revealed to Rodimus that Guiltar was built using the combined skills and essences of Optimus Prime and Megatron, making him a most formidable adversary. With no other choice but to cooperate, the two faction leaders teamed up against their new common foe. Rodimus transformed into vehicle mode and rammed the unsuspecting Guiltar, Galvatron following-up with a blast in cannon mode. The two then joined in a combined "Galvatron/Rodimus Kick", destroying Guiltar's body. Much to their surprise, Starscream's ghost floated free of the shattered chassis. As if to rub it in his face, Rodimus reminded Galvatron that, obviously, the Quintessons could not be trusted. The two went their separate ways for now, both too weak from Guiltar's attacks to continue the fight.
Trivia
Mega-mouth!
Guiltar's preliminary head design did not feature Optimus Prime's faceplate; effectively, he looked like Megatron wearing an Optimus hat!