Whether he was born from the fires of Unicron himself, or was an ancient Transformer warlord, or something else altogether, one thing is always certain: Galvatron is a focal point of power and madness given form. He is blind to all but his lust for power; his whims and desires can be sacrificed in a moment's rage. Not even his own subordinates are safe. Though he is not beyond the capacity for long-term goals, it is his unpredictability and his casual disregard for any and all life that strike such horror in friend and foe alike. Truly, the Decepticon leader is without any sense of empathy.
In most universes, Galvatron was once Megatron, but was reborn from his death throes in a Faustian pact with Unicron. He retains the memories and spark of Megatron, but his personality was significantly altered after the near-death experience, massive physical upgrade, and reprogramming; just ask Starscream about the difference. And all that was before he went insane. The cause and extent of Galvatron's madness varies between different timelines, as does his physical power. Sometimes he's all but invincible.
He has been voiced by David Kaye and Frank Welker, just to name a couple.
Legends of the Multi-Universe (Menslady's story)
After infusing the Black Crystal of the Decepticons, which carried the powers of Unicron and Jack of Blades, to himself, Megatron was transformed into his powered-up identity: Galvatron. At this point, he is more determined than ever to capture the Angels, get Myotismon back on his side, destroy Disney, and take control of the universe.
At present, Galvatron seems to have been successful in his plans by taking Myotismon and Angewomon, but stooping to a SERIOUSLY new low by disguising himself as Emperor X's deceased father and then abducting the Angels. Can the Children of the Autobots save them or will he destroy them all?
The Chaotic Wars
Galvatron revealed himself to be a Warrior of Harmony and aided Myotismon and Menslady in a battle against Machinedramon and some other Digimon. Sadly, he was badly injured in battle and murdered by Emperor Mateus. His loss inflicted great emotional pain on both Myotismon and Menslady, since he loved them as if they were truly his own offspring.
However, at the end of season 4, it was shown that he had returned. At the start of season 5, it was revealed that he faked his death. No doubt Myotismon is very happy, but it is not clear yet as to how Menslady/Angewomon is feeling.
The Protectors of the Multi-Universe
Galvatron has returned with the other revived villains and is determined to have revenge on the Angels and take control of the Multi-Universe. Hera fearfully suggested that she could rule at his side, but Galvatron would NOT have that! Instead, he revealed that he had taken a liking to Morgana...and devoured Hera's soul!
However, Galvatron has said that Morgana will be ONE of his queens. It does not take a genius to figure out whom he intends to take as another!
As usual, he has crossed the moral event horizon...this time by capturing friends of the Autobots, Angels and Protectors unless they surrender to him. He also has plans for killing said friends...even his offspring, RedFlame and Majingirl!
But that is not all. He has taken Walt Disney and a ton of the Children of the Autobots and placed them in crystal prisons in order to absorb their powers, then let them recover...only to drain them again!