Galvatron began his function cycle as the mighty Decepticon warrior Megatron, commander of the Decepticon army. In the Earth year 2005, Megatron led an attack on Autobot City, the Autobots' base of operations on Earth, and had his final confrontation with Optimus Prime. Megatron inflicted mortal damage to Prime, but in his death throes, Prime returned the gesture, knocking the already-damaged Megatron two stories down from their battlefield. The Decepticons fled into space, but Astrotrain, who was carrying them all in his space shuttle mode, demanded that they "jettison some weight" or else he couldnt make it back to Cybertron. The treacherous Decepticon Air Commander, Starscream then had all the weakened and injured Decepticons thrown from Astrotrain - Megatron among them.
While floating in space, Megatron and the other Decepticons were recovered by Unicron, the monster planet, who extended an offer to Megatron - if Megatron destroyed the Autobot Matrix of Leadership, Unicron would give him a new body, and new troops to command. Megatron reluctantly accepted. Thundercracker and Skywarp were changed into Scourge and Cyclonus, the Insecticons became the Sweeps and the armada, and Megatron himself became the even-more-powerful Galvatron.At this time, Galvatron was completely sane, and fully aware of his former existence. He led an attack on Earth, and forced the surviving Autobots, led by Ultra Magnus to flee into space. Magnus and his crew temporarily decieved the Decepticons into thinking they had been destroyed, and set down on the planet Junkion to repair their damage shuttle. However, Galvatron and his forces soon caught up to them, and Galvatron stole the Matrix from Magnus, planning to use it to subjugate Unicron. When this plan failed, Unicron, who had now transformed to his gigantic robot form, consumed Galvatron, and initiated his assault on Cybertron. The young Autobot, Hot Rod, also voyaged inside the planet-eater, but was separated from his companions, and wound up battling for his life against Galvatron. As Galvatron was about to strangle him, Hot Rod grabbed the Matrix, which was suspended from Galvatron's own neck.
It's power transformed Hot Rod into the new Autobot leader, Rodimus Prime. Rodimus simply picked up Galvatron, and hurled him through Unicron's hull, into the void of space. Unicron was subsequently destroyed by the power of the Matrix.
Galvatron is armed with a particle cannon, mounted on his right arm. It has incredible potential for destruction, which is magnified when Galvatron transforms into his laser cannon tank mode. At first, Galvatron was a ruthless, cunning, completely sane, yet impossibly evil commander, but, as we shall see, that would soon change.
In the year 2006, the Decepticon forces, now without Galvatron to lead them, retreated to a sterile planet known as Charr, with rapidly dwindling Energon reserves. Cyclonuc rationalised that they must find Galvatron, and he, Scourge, and the Sweeps, travelled to Unicron's head, which was still intact, and orbiting Cybertron as a moon, where they activated his data banks, and viewed the final battle between Rodimus and Galvatron. Plotting Galvatron's course as he was thrown into space, they quickly tracked him to the planet of Thrull. They found him, trapped in a pool of plasma lava, with only his hand jutting out of the dangerous ooze. When they retrieved him, one of the Sweeps made a quick and accurate analysis - "That plasma bath fried Galvatron's circuits". The Sweep, it turned out, was completely correct. The plasma lava had seeped into Galvatron's cranial case, furthering damaged done when Rodimus hurled him head-first out of Unicron, driving him completely and utterly insane, and also altering his vocal circuits unrecognisably. Galvatron made a deal with the Quintessons, the five-faced aliens who built the first Transformers, to attack and reclaim Cybertron, but when he found out that they had lied to him about the existence of a Decepticon Matrix, he turned on them, and the day was lost.
While Galvatro was able to concieve some decent plans in his more lucid moments, Cyclonus realised he was dangerously unhinged, and took him to the planet Torqulon, in hopes that the famous therapists there could cure him. Galvatron didn't accept the treatment to say the least, and went on a psychotic rampage.When Optimus Prime was restored to life, Galvatron was one of the last Transformers to succumb to the Hate Plague, but not before he gave Prime the heat-resistant alloy he had previously stolen, that held the key to defeating the Plague. Once Prime used the wisdom inside the Autobot Matrix to cure the madness of the plague, Galvatron declared: "There will be no war this day, Optimus Prime. You have earned Galvatron's respect". However, some months later, Galvatron led every single Decepticon in the known universe on an attack on Autobot City, and stole the Plamsa Key - the device that would open the Plasma Energy Chamber on Cybertron, so that the energy contained within could power the Decepticon forces. However, a small group of Autobots reclaimed the key, but energy from the already-opened chamber overloaded their ships engines, sending them hurtling away from Cybertron, to crash on the planet Nebulos. They were quickly followed by Decepticons. Both teams linked themselves with the planet's inhabitants, to become Headmasters and Targetmasters, to effectively battle eachother. Upon discovering this, Galvatron was outraged that his followers had linked with flesh creatures, but still formed an uneasy alliance with the Hive (a group of evil Nebulons) and their leader, Lord Zarak. The Plasma Energy Chamber was once again opened by the Decepticons, after stealing the key back from the Autobots, and Galvatron directed the energy into the sun, to force it to go nova. The two gigantic Headmaster cities, Fortress Maximus and Scorponok, were engaged in battle at this time, but Fort Max quickly defeated Scorponok, and he and the other Autobot Headmasters and Targetmasters headed for Cybertron, where the human, Spike Witwicky, with the aid of Fortress Maximus, rerouted the surplus energy from the sun back to Cybertron, restoring its Golden Age. The resultant energy backlash from the chamber sent Scorponok, and every other single Decepticon and Hive member inside him, hurtling millions of miles away from Cybertron, through space. Galvatron has not been seen or heard from since, but it seems obvious that he would still be functional, plotting his takeover of the universe... provided Lord Zarak does not accomplish that goal before him.