X, better known as Sonic.exe (sometimes stylized as Sonic.EXE), is the titular main antagonist of the infamous Creepypasta of the same name and its sequel Round 2.
He is an anomalous, interdimensional energy-based entity driven by an instinctive lust for destruction and pain. Becoming completely obsessed with enslaving the human race, X took the form of Sonic the Hedgehog and created a haunted copy of the original Sega Genesis game that acted as a portal separating his dimension from Earth. Since then, he's been using his cult to pass down the game from victim to victim, hoping to one day use it to merge the two realms together and rule the human world and other worlds as a god.