A gladiator would name himself after Megatronus before shortening his name to simply "Megatron". According to legend, at the beginning of time, Unicron and Primus battled each other for eons, with neither side remaining victorious for long. Until, that is, Primus created the Thirteen. These Thirteen defeated Unicron and cast him into space.
At some point statues of Megatronus Prime and his brothers were made. They were placed in the chamber of the High Council.
According to slides shown at BotCon 2010, Megatronus is a large, dark robot with a Decepticon symbol-inspired head. He wields a red and black fusion cannon and is known as the Warrior of Darkness to Prima's Warrior of Light. As the Fallen, his body is shrouded in flames.==transformers prime==
took the legendary name Megatronus as his own, he called for an end to Cybertron's decrepit caste system and told the downtrodden that freedom of self-determination was the right of all sentient beings!
But absolute power corrupts absolutely, and Megatron's Decepticon revolution, like many such movements, ended up becoming a whole new tyranny. Powerful, charismatic, violent, and full of rage for any who would stand in the way of his ambition and drive, Megatron brought Cybertron past the brink of destruction. Now he and his former brother-in-arms Optimus Prime fight on other worlds. Megatron will never forgive Optimus for "betraying" him, stealing from the Council the rank of Prime which was rightfully his. He has reserved for his old friend the greatest honor possible: glorious death at his hands.