Megatron was a six-changer, able to transform into five additional modes aside from his robot form - a twin-headed dragon, a bat-gargoyle creature, a race car, a spaceship,and a claw. After becoming Galvatron, he gained an additional four modes, including a hydrofoil, a griffin, a pterodactyl, and an elephant. He also has the ability to absorb energy from other lifeforms, making him an "energy vampire". Each form has its own different frightening capabilities, making Galvatron a very unstable and unpredictable fighter.
A Predacon warlord before coming to Earth, Megatron is believed to have decimated numerous planets in his quest for energy. Optimus stated that Megatron left entire planets as "lifeless barren rocks". Under orders from the Predacon Council, Megatron came to Earth to seek the huge Autobot battle station, Fortress Maximus, while under a cover story that he was simply looking for energy. His first appearance was at the International Scientific Symposium in New York, during which he and the Predacon trio fought Optimus Prime and the Autobot Brothers. Although the battle did not go well, Megatron was able to abduct Doctor Kenneth Onishi, an energy expert and archaeologist. Doctor Onishi was subjected to the psycho-probe proved to be slow work in extracting information. In the meantime, Megatron sent his minions out to steal energy to refuel their ship, the Megastar, only occasionally venturing out himself to help them.
During their many attempts to seize energy did not go well, as they were continually thwarted by the Autobots. These included Sky-Byte failing to capture a bomb, the Spychangers swapping out the Plutonium Energy Generator for a fake, and many more. At one point, Megatron sought to activate the Black Pyramid, an ancient ruin which he claimed to have known about long before the humans. As the Predacons prepared to tap into the Black Pyramid's power, a ship entered the area. Fearing that it would draw the Autobots’ attention, Megatron ordered Sky-Byte to take it out before it got any closer. Of course, attacking the ship did nothing but bring the Autobots onto the scene faster. As the Predacon's mission went south, Megatron decided to destroy the Black Pyramid rather than allow it to fall into anybody else's hands.
After several more failed missions, the interrogation of Dr. Onishi finally saw results in the discovery of a crashed Autobot spaceship in America. Megatron was able to snatch six protoforms from the ship and took them to the nearby McKinley Army Base where he imbued them with energy from his spark, reformatting them into the Decepticons. Eager to test his new troops, he sent them to destroy Sherman Dam and hacked into the primitive human television transmissions in order to extort the humans in the nearby city of Los Bogus into surrendering. Unfortunately, things did not go well and Megatron was left looking embarrassed in front of all the humans.
Megatron began seeking the mysterious O-Parts, which led to the Orb of Sigma, in a subterranean pyramid. The orb would lead to Cerebros, the power key to Fortress Maximus. When Megatron was buried in the ruins of the pyramid following a failed attempt to steal the orb from the Autobots, he underwent his most startling transformation of all, as the energies of the pyramid resurrected him as the vampiric Galvatron, able to enhance his own strength by draining the life energy from others, starting with the Predacon Trio. Upon arriving in Metro City, he claimed that Megatron was dead and that he was a new person, claiming to now be a Decepticon. Galvatron drained the energy of Fortress Maximus and engaged Omega Prime in a final battle at the Earth's core. Prime was able to defeat him with the gathered energy of Earth's children, courtesy of Fortress Maximus, and he was sent back to Cybertron for imprisonment.
- In the Japanese version of Robots in Disguise, Car Robots, Megatron is a separate character, called "Gigatron", with the Galvatron form being called "Devil Gigatron". Whenever this character has been brought into another continuity, which usually have their own Megatron's, he goes by the name Gigatron.
- This separation helped in Car Robots being retconned into the Japanese version of the G1 cartoon timeline.