Megatron is a character from the Transformers franchise, created by Hasbro in 1984, based on a toy design by Takara. The original Megatron was the Decepticon Leader, which could transform into three different types of guns; a Walther P38 handgun, a particle beam cannon, and a telescopic laser cannon. He is a sentient robotic lifeform from the planet Cybertron and the leader of the villainous Decepticons as well as the archenemy of the Autobot leader Optimus Prime.
Megatron is usually depicted as having risen up from the lowly worker to become a champion in gladiatorial combat. As a gladiator, he took the legendary name "Megatronus" as his own and would similarly inspire a later villainous character. He called for an end to his planet Cybertron's corrupted governing body and told the downtrodden that freedom of self-determination was the right of all sentient beings, becoming a mentor to the young Optimus Prime. Prime would later use his teachings against him when he became corrupt. He has the ability to transform between his robot shape and various weapons or vehicles, but these "alternate-modes", his origins and even personality, can vary depending on which "universe" he's seen in. This origin is considered the most consistent between the various incarnations. Further differences are listed in the respective sections below.