Megatron is the main antagonist in Beast Wars and Beast Machines. A descendant of the original Megatron who led the Decepticons during the Great Cybertronian War, he modelled himself after his namesake and sought to succeed where the former had failed: to lead all of Cybertron down the path of conquest and dominate the entire universe. Throughout both series, he was voiced by David Kaye.
History
Pre-Beast Wars
Megatron was originally a Predacon terrorist who worked under crime-lord Cryotek. Shortly before his exodus to prehistoric Earth, he carried out the theft of an ancient artifact known as the Golden Disk (which was actually the data disk from the Voyager 1 space probe) which contained information vital to the Predacons' conquest of Cybertron. Studying the information it contained, Megatron betrayed Cryotek and assembled a crew to aid him in a bold endeavour: to travel back in time to prehistoric Earth during the period when the Autobots and Decepticons were in stasis lock within the Ark. There, Megatron would attempt to alter history to ensure that the Decepticons would win the Great War and dominate the universe.
Beast Wars
After acquiring the Golden Disk and a transwarp drive, Megatron and his Predacon crew fled Cybertron aboard their commandeered starship, the Darksyde. The Maximal survey ship Axalon, captained by Optimus Primal, was redirected from its research mission and ordered to pursue the fugitives. The Maximals pursued Megatron into transwarp space and both ships emerged in close proximity to Earth, 3 million years in the past. Both Maximal and Predacon ships crash-landed, but when they emerged to survey their surroundings, it appeared that Megatron had brought them to the wrong planet. In the sky were two moons and the landscape was littered with raw, crystallized energon. While energon served as the basic fuel for Transformers, in this state and in such quantities it proved to be dangerous to them, threatening to overload their systems and send them into stasis-lock. To compensate, both Maximals and Predacons were forced to take on semi-organic beast modes to protect them from the energon radiation. In Megatron's case, he took on the form of a tyrannosaurus rex after scanning the fossilized remains of one of the extinct creatures.
With energon resources abundant on this planet, the Maximals feared that Megatron was planning to harvest it in order to start another Great War. They had no idea what his true intentions were. The Beast Wars raged as both sides fought over energon, stasis pods containing Maximal protoforms and strange alien relics left behind by unknown beings (later identified as the Vok). Among these alien artifacts was a disk similar to the one Megatron had stolen on Cybertron which contained information relating to the aliens' activities on the planet. Megatron had hoped to acquire the aliens' technology and use it to fulfill his mission, but because of the Maximals' interference the alien disk was lost.
Megatron's Transmetal body
While Megatron had lost access to the technology of the Vok, he realized that he had indeed arrived on prehistoric Earth as planned. One of the moons in orbit had been revealed to be an alien superweapon (which was promptly destroyed) and a tribe of primitive humans was later discovered. The Tripredacus Council - the ruling body of the Predacon Alliance - had also become aware of Megatron's successful voyage through time and had sent one of their covert agents - former Decepticon Ravage - back in time aboard a transwarp vessel to find Megatron and arrest him. However, after Ravage assisted the Maximals in capturing Megatron, the Predacon rogue showed Ravage the content of a fragment of the shattered Golden Disk: a partial message from the original Megatron, Ravage's old commander. The message was a back-up plan in case the Decepticons were defeated by the Autobots, which they were, and was intended to inspire Megatron's descendants into ensuring Decepticon victory by altering history. Realising that Decepticon dominance could yet be achieved, Ravage switched sides and joined the new Megatron, using his ship to attack the Maximals and destroy their base. However, Ravage and his ship were destroyed from within by the Maximal Rattrap. Despite that setback, Megatron now knew how to find the Ark.
Predacon turncoat Blackarachnia had downloaded Megatron's private datatrax prior to her desertion and had gone in search of the Ark. Megatron followed and forced her to open the ancient ship, allowing him to enter and fulfill his mission: to assassinate the stasis-locked Autobot commander Optimus Prime. Without their leader, the Autobots would lose the Great War and the Decepticons would conquer Cybertron and the entire universe. This plan was also thwarted when the Maximals used the Ark's main computer Teletraan I to repair Optimus Prime's body whilst Optimus Primal stored the legendary Autobot's spark within his own body, briefly bonding it with his own spark which resulted in the Maximal leader undergoing another Transmetal transformation.
Megatron's Transmetal 2 form
Megatron did not rest. He went on to reverse-engineer alien technology, gained by means unknown, to create the Transmetal 2 process and create himself a loyal clone of Dinobot. He also worked towards taking control of Optimus and seizing control of the new Maximal base, allowing him to enter the Ark again. Wanting to replicate the effect Optimus Prime's spark had on Primal, he deliberately took the spark of the original Megatron and placed it in his body. He was transformed into a powerful dragon and able to give Optimus Primal a sound beating, until chased away by the recovered Maximal group.
Shortly after gaining his Transmetal 2 mode, Megatron and the Predacons received an unwelcome visit from Tigerhawk, a Fuzor of the lost Maximals Tigatron and Airazor sent by the Vok. Tigerhawk destroyed the Predacon base and was later confronted by the Maximals who managed to restore the fused consciousness of Airazor and Tigatron, breaking the Vok's control.
Having seemingly lost everything, Megatron and the remaining Predacons investigated the abandoned lair of the deceased Tarantulas for anything of value. There, Megatron had discovered that Tarantulas had found the Nemesis, the Decepticon warship that had pursued the Ark to Earth and presumably been lost. Megatron found the ship, seeing that Tarantulas had repaired and enhanced it, including fitting it with a transwarp drive, and he decided to use the mighty dreadnought to travel back to his own time and conquer Cybertron. But first, he decided to use the Nemesis to finish off Optimus Primal and his Maximals as well as destroy the Ark.
Primal and his team survived the Nemesis' attack and Primal battled Megatron once again aboard the warship's bridge. With the help of Dinobot II, who had inherited his predecessor's sense of honour, Optimus defeated Megatron and crashed the Nemesis into the ocean, thereby preserving history. The Maximals then captured Megatron and removed the spark of the original Megatron from his body, putting it back into the Decepticon leader's prone body within the Ark. Using a spare Autobot shuttle that history had overlooked, the Maximals left Earth and returned to their own timeline thanks to the salvaged transwarp cells from the Nemesis. The Beast Wars were finally over and Megatron was further humiliated by his foes as he was strapped to the outer hull of the shuttle as it took flight.
Beast Machines
During the Maximals' flight through transwarp space, Megatron was able to break free of his restraints and found himself catapulted through the transwarp corridor ahead of his enemies. Arriving back on Cybertron, he used the window of opportunity for maximum effect, releasing a virus across the planet that quickly incapacitated the population. He then began extracting the victims' sparks and storing them in a citadel, planning to one day absorb them into his own spark. Meanwhile, he used factories to rebuild the bodies into mindless drones he called "Vehicons." Eventually, he had every spark on Cybertron in his possession.
Clearly Megatron had changed since the Beast Wars, not only in his goals, but also in his mannerisms. Gone was the ham who sought conquest for the sake of glory and power and the Predacon cause. He spoke not of revenge on the Maximals, but rather of the liberation of all Transformerkind from the chaos of free will. He referred outright to his own ascension to godhood and he had also developed a sense of honour, keeping his word to his enemies even at the risk of future losses. During the Beast Wars, he had positively reveled in his dinosaur and dragon beast modes. But on his return to Cybertron, something convinced him that beast modes and other vestiges of the organic were an abomination which should be scoured from the planet, leaving only technological purity. Despite his pontifications, Megatron himself had not achieved the "purity" of which he spoke. His dragon form remained, and at times, it overwhelmed his control. His unfruitful attempts to remove the organic elements from his own body became a source of constant frustration. This was a new and even madder Megatron.
When the Maximals arrived in their shuttle, they found the planet empty aside from Vehicons who immediately attacked them with canisters of a gas that infected them with the virus. The fully-Transmetal among them "devolved" into their original beast modes but were able to keep moving and escape. The remaining two, Rhinox and Silverbolt (who never received any form of upgrade on Earth), were instead paralyzed and quickly overtaken. Their sparks soon joined Megatron's collection.
The escaped Maximals would have succumbed to the virus eventually if not for the Oracle reformatting them. This was the beginning of Megatron's undoing, for their new technorganic bodies were both immune to the virus and (while in beast mode) invisible to Vehicon sensors. Megatron's first resulting change in strategy was to imbue three Vehicons with captured sparks so they could think on their feet in battle. The original personalities of these "generals" were deeply buried under shell programs, which allowed Megatron to use sparks of the Maximals' former allies. Thus, if the Maximals discovered who they really were, they would be reluctant to destroy them. The recently-captured Silverbolt and Rhinox were made into Jetstorm and Tankor, respectively. The third general, Thrust, was created from the Predacon Waspinator for reasons that remain opaque.
Megatron considered using the same technology on himself, transferring his own spark to a "pure" Vehicon body. But he decided it not worth the risk to expose his spark, however briefly.
Noble
Rhinox eventually awakened and went rogue, planning a grand scheme to usurp Megatron's dominance, but Megatron effortlessly seized control of his traitor-general's evil plan at the last minute and almost wiped out all resistance with the Key to Vector Sigma. At the last moment, Optimus unleashed the Plasma Energy Chamber force and the combined energies destroyed Megatron's body. He was presumed dead, but the combined energies had actually succeeded in separating his organic half from his body—unfortunately, his spark went with it and was now trapped in a purely organic Transformer. He took the identity of "innocent" Maximal Noble and, preying on Nightscream's survivor guilt and Optimus's inherent goodness, got the Maximals to help transfer his spark to the Grand Mal, a vessel in the shape of his own head.
With Tankor destroyed and Jetstorm eventually reformatted into Silverbolt, Megatron used the sparks of famous generals Obsidian and Strika to replace them. He also managed to gain a link to the Oracle itself, stealing the knowledge from Primal. This gave him the ability to move ahead with his grand plan—to consume the captured sparks and eventually consume/replace the Allspark itself—but Nightscream temporarily stopped him by depolarizing Megatron's own spark. Now severed from a body, it jumped between discarded shells and attacked everyone in a zombie-like fashion. Rattrap would use a spark extractor to repolarize his spark, allowing Megatron to regain his senses, but trapping him in a Diagnostic Drone.
Immediately following this, Megatron launched an all-out battle for the sparks and succeeded in capturing them, as well as the sparks of all the Maximals and obliterating their technorganic orchard—leaving just Optimus Primal and himself as the only two Transformers on the entire planet. To add insult to injury, he uploaded his spark into a copy of Primal's old Optimal Optimus form. Over the conflict, his personality had gradually become more like that of his Beast Wars self, and by this point he was once again hamming it up—revelling in his victory, mocking his enemies (his stated reason for copying Optimus' old body) and deliberately not killing Optimus outright, and having melodramatic outbursts when in his new body.
At the end of a fierce one-on-one fight, Megatron won and began consuming his amassed sparks, growing ever more powerful and planning to become both the new Matrix and the new core consciousness of Cybertron. However, he'd made his old mistake—leaving Optimus alive (to make him watch his "ascension") instead of killing him. When he attempted to use the Key to Vector Sigma to transform the planet's organic core into technomatter, Primal managed to dislodge them both. They plummeted into the planet's liquid core and from there, Primal was able to reformat the entire planet, destroying himself and Megatron completely, but freeing all the lost sparks to repopulate their newly redecorated planet.