Gilthor
Guiltar was a Quintesson creation from the Generation 1 series.
Guiltar 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.
Fiction
2010 Manga
Guiltar rose from the sea off of Japan, seeking out Rodimus Prime and Galvatron, who were in the area about to face off in another duel. Guiltar attacked Rodimus with a variety of artillery modes, sending the Autotbot leader flying. But as Galvatron gloated over his fallen enemy, Guiltar snuck behind him and attacked, savagely beating Galvatron and kicking him to where Rodimus had fallen.
Down, the two faction leaders teamed up against their new common foe. Rodimus transformed into vehicle mode and rammed Guiltar, Galvatron following up with a blast in cannon mode. The two joined in a combined kick, destroying Guiltar's body. Starscream's ghost floated free of the shattered chassis, and the two leaders realized they still had the Quintessons to deal with.
