The Decepticons who built the memorial for Galvatron were presumably aware that the warlord was not dead, but what they didn't know was that he had reformed himself into a new and improved version of himself. When he seized one of the energon cubes that surrounded him, a massive energon explosion triggered a transformation sequence that merged him into the all-new Galvatron!
Galvatron's original form was a colossal robot with a turret and huge fusion cannon. But the new Galvatron is a sleeker, more agile machine with an impressive array of weapons. He's also a much more ruthless and cunning warlord than his predecessor.
Although the 1987 animated film depicted Galvatron with his later head design and cannon, the new Galvatron's design was still a prototype. The design would go through several revisions before it was finalized for the movie.
After a few years of Galvatron leading the Decepticons, the character grew increasingly corrupted and twisted, which led to him betraying his own faction to the Autobots. The Autobots eventually defeated him and his henchmen, but it was too late: Galvatron had already time-travelled back to 1987 Earth and conquered the world!
Whether he's born of the fires of Unicron, an ancient Transformer warlord or his own self-destruction, Galvatron is pure madness given shape. His single-minded pursuit of power is blinding to all but his lust for destruction, and no one is safe from his sudden outbursts of rage.