Dark Nova
Dark Nova was a mysterious supernatural entity from outer spcae who sided with the Decepticons during Battlestars. He revived Galvatron, upgrading him into Super Megatron, and eventually merged with him to become the Star Giant.
Fiction
Battlestars manga
Little is known about the origin of Dark Nova (though he does bear a striking resemblance to The Vok), however, he was a very powerful supernatural entity who favored the Decepticons. Using his vast powers, he revived Optimus Prime's body without a Spark, resulting in the evil False Convoy. False Convoy was eventually subdued by the Autobots, the Zodiac placed in his chest, reviving him as Star Convoy.
To counter the threat of Star Convoy, Dark Nova did one better. Recovering the frozen corpse of Galvatron from its icy grave in the North Pole (where Galvatron met his fate during Headmasters), Dark Nova used his talents to resurrect and upgrade Galvatron into Super Megatron. Super Megatron then lead the Decepticons forces (including a legion of drone warriors and the city-transformer, Metrotitan) into battle against the Autobots.

Eventually, Star Convoy defeated Super Megatron, resulting in Dark Nova providing another upgrade; this time into Ultra Megatron. Ultra Megatron was ultimately defeated, as well. Irritated, Dark Nova merged with Ultra Megatron, resulting in the Star Giant. He proved a magnificent adversary, but in the end, Star Convoy triumphed over Star Giant, destroying him. While Megatron managed to survive the destruction of Star Giant, Dark Nova did not.
Note
Early design sketches for the Battlestars showed "Dark Nova" to actually be Unicron. Either that, or he was intended to be Unicron the whole time. In reality, Unicron was simply used as a "place-holder" until the artists and writers could design a new villain. Unicron does not appear in any of the released Battlestars story pages and thus is not a part of the story.

