Transformers: Cybertron
Ten years later, Primus's plan to imprison Unicron's spark at the heart of the sun ultimately failed, leading the star to collapse, creating a black hole which threatened the existence of Cybertron, and the rest of the universe. Escaping his confinement within the sun, Megatron (now known as Master Megatron in Japan) enhanced his powers by merging his body with the remnants of Unicron's shattered form, increasing his power with the dark god's own. In this new form, Megatron became a Triple Changer with the ability to change into a monstrous racing vehicle and a Cybertronian jet plane. His primary weapons consist of two rear-mounted missile launchers and the ability to unleash energy streams from his palms in the shape of lightning bolts. In addition, he can call upon a Cyber Key to activate high speed thrusters in vehicle mode, as well as a battle claw (Named as Death Claw in Japan) in robot mode.
As the Autobots prepared to evacuate Cybertron in the wake of disasters caused by the black hole, Megatron struck, approaching the unprotected ancient Transformer Vector Prime, and stealing a holographic map containing locations of the Cyber Planet Keys that could be used to seal the Black Hole. Operating out of a fiery pocket dimension, Megatron schemed to used the power of the world-shaping Cyber Planet Keys and their focal Omega Lock to accelerate the universal degeneration created by the black hole, destroying the universe and using the keys to remake it in his own image.
Leaving Starscream and Thundercracker to search for the Omega Lock on Earth, Megatron located the resting place of the first Cyber Planet Key on Velocitron, the Speed Planet. Recruiting the native troublemakers Ransack and Crumplezone to do his bidding, he deduced that the planet's racing trophy was the key. After failing to defeat planet ruler Override in a race to learn more, however, he left Ransack and Crumplezone to compete in tournaments and win the trophy and turned his attention to the Jungle Planet, home of the second Cyber Planet Key, where he ingratiated himself with planet ruler Scourge. Both missions ultimately ended in failure, however, when the Autobots acquired the keys.
Attempting to find the third key, Megatron discovered that he had been betrayed by Starscream when the planet map - in reality, a duplicate switched out by Starscream - led him to a dead sector of space and sealed him within a metallic sphere. Scourge was able to liberate him a short time later, but in that time, Starscream had obtained the third Cyber Planet Key, from Earth, for himself, along with the Omega Lock and other keys. Megatron made a beeline for his treacherous lieutenant, but was intercepted by the Autobots Hot Shot, Red Alert and Scattorshot, who intended to hold him off until the other Autobots could stop Starscream. Starscream's attempts to harness the Earth Key, however, caused a release of its energies which endowed Megatron with a new Cyber Key power - the Death Machine Gun, which he used to mow down the Autobots in his path.
The Autobots managed to retake the keys from Starscream, but a further attack from Megatron saw the Decepticon leader steal them out from under Optimus Prime's nose and retreat into his pocket dimension. Prime pursued him through the portal and defeated him in a pitched battle, reacquiring the lock and returning to Cybertron. As Megatron attempted to follow him, Vector Prime combined his portal-opening powers with the Cyber Planet Keys and collapsed Megatron's dimension in upon itself, destroying the villain.
This was not to be the end for Megatron, however, as the power of his Unicron armor sustained him as a ghost-like entity composed of pure darkness. In this state, he rematerialized on Cybertron and used Unicron's reformatting powers to upgrade the injured Crumplezone into Dark Crumplezone. As he came under attack from the Autobot Leobreaker, his regeneration completed and his physical body was restored, even as he used the remainder of the lingering darkness to create an evil doppelgänger of Leobreaker, Nemesis Breaker, out of the Autobot's own dark thoughts. Merging with Nemesis Breaker to form Dark Claw Mode, Megatron battled Optimus Prime and Leobreaker's Savage Claw Mode and made a further play for the Omega Lock, until news of the location of the fourth and final Cyber Planet Key led him to withdraw.
Guided through a spatial warp by the mysterious Soundwave to Gigantion, the Giant Planet, home of the final key, Megatron engaged the world's leader, Metroplex, in battle. Much to his surprise, however, he was utterly defeated in seconds, and Nemesis Breaker was destroyed. Consumed with rage, the power of Unicron within his armor reached out and detected the energies of the Giant Planet's Cyber Planet Key, drawing upon them and infusing Megatron's body with them. Attacking the Autobots in a dark, shadowed form, he decimated most of their forces before being confronted by Optimus Prime and completing his transformation - once again, Megatron had become Galvatron (Master Galvatron in Japan).
After taking revenge on Metroplex, Galvatron joined the race to acquire the Giant Planet key, which included a rematch with the reborn Hot Shot, Red Alert and Scattorshot. Yet again, the Autobots were able to acquire the key, but Galvatron then stole the completed Omega Lock, only to be attacked by Starscream, who battled with Galvatron for possession of the artifact. Galvatron ultimately claimed victory in the battle, with the sheer amount of energy released in the clash actually blasting Starscream into another universe. With the lock and keys now in his hands, Galvatron returned to the Black Hole, where he was eventually confronted and finally defeated by the five planet leaders regardless of his new powers that supersized himself and his troops.
Having had ultimate power torn from his grasp, Galvatron contemplated giving up, but when Starscream's spirit reached out to him and goaded him into continuing his vendetta, he challenged Optimus Prime to one epic final duel. The battle was long, and eventually ended on Cybertron's moon. Galvatron almost won when he generated a massive blade of dark energy, which Prime countered with Vector Prime's sword. As the two old enemies charged towards each other in a final strike, Optimus Prime impaled Galvatron, whose body crumbled and dissolved as he met his end once and for all.
In a montage sequence at the conclusion of the series, however, Galvatron's evil proved eternal, as, beyond the veil of time and space, his spark battled with that of Vector Prime.
Galvatron's power in this series was very inconsistent. He was clearly more powerful then Optimus in his first appearance, but was evenly matched with him in their final battle.
Read more about this topic: Galvatron, Unicron Trilogy, Animated Series