Megatronus, also known as Megatronus Prime or the Fallen, is an ancient and immensely powerful Cybertronian introduced in the 2015 animated series Transformers: Robots in Disguise. He originates as one of the original Thirteen Primes, the first Transformers created by the entity Primus to battle the chaos-bringer Unicron. Unlike his brothers, Megatronus was designed as a dark warrior attuned to entropy and destruction. His inherently volatile nature ultimately led him to commit the first murder on Cybertron: he killed his fellow Prime and beloved Solus Prime. This act of betrayal caused him to be branded the Fallen and exiled to another dimension for eons. In the series, Megatronus serves as the true main antagonist of the first season. He orchestrates the crash of the Alchemor, a Cybertronian prison ship, onto Earth, deliberately freeing hundreds of Decepticon prisoners to cause chaos and weaken his enemies. He blackmails the cunning Decepticon Steeljaw into helping him escape his dimensional prison, using Steeljaw's pack as pawns. Once free, he seeks to destroy both Earth and Cybertron, driven by a burning desire for vengeance against the universe he believes wronged him. His personality is marked by immense pride, a deep sense of betrayal, and a cold, calculating ruthlessness. Despite being a Prime, he fully embraces his role as the first Decepticon, viewing himself as superior to all others and displaying no remorse for his crimes. He is manipulative and commands loyalty through fear and force. Megatronus's key relationships include his former brothers among the Thirteen Primes, who eventually prepare Optimus Prime to oppose him. His murder of Solus Prime is a defining wound, both for him and for the other Primes. He also has a significant adversarial relationship with Steeljaw, whom he uses and discards, and with Optimus Prime and Bumblebee, who lead the team that ultimately confronts him. In terms of development, Megatronus remains a largely static figure, a force of ancient evil whose defeat is necessary for the Autobots to grow. His defeat comes when Bumblebee, Sideswipe, and Strongarm combine their weapons into a powerful energy beam that seemingly destroys him, allowing the team to finally subdue him and his allies. Megatronus possesses formidable abilities. He wields dark science and gravitational powers, and he carries the Requiem Blaster, one of the most dangerous artifacts in Cybertronian history. He is physically imposing and nearly indestructible, with his face serving as the inspiration for the Decepticon faction insignia that would later be adopted by his ideological successors. He can also generate fiery energy and withstand tremendous attacks. Despite his defeat, his legacy as the original betrayer and the first Decepticon endures in the mythos of the series.