Guiltaur, 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.
The Transformer manga
Guiltaur 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 Guiltaur 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 Guiltaur's obedience, Guiltaur snuck behind him and attacked, savagely beating Galvatron and kicking him to where Rodimus had fallen. Revealing his true intentions, Guiltaur was gunning for leadership of the Decepticons, which even a concussed box turtle could have seen coming. But not Galvatron.
Down, Galvatron revealed to Rodimus that Guiltaur 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 Guiltaur'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 Guiltaur's attacks to continue the fight.
- Guiltaur's preliminary head design did not feature Optimus Prime's faceplate; effectively, he looked like Megatron wearing an Optimus hat! The early name of Guiltaur in the conceptual art is called "Convotron", which derives from "Convoy + Megatron".