The Birth of Exe
Few people across the multiverse knew the entity known simply as Exe, and even fewer had made various speculations. Some claimed that it's a form of Satan or at least a powerful demon from Hell, and others believed that that it was God itself. But this particular creature is none of those things. In fact, it isn't even a creation of God or the Devil. He's an entirely different entity, one that created itself.
See, this entity that is was created in the void, in a gap between dimensions, making it a non-existent outsider to most if not all universes. Exe was born out of pure dark matter in this void, and at the time it had no real namesake nor did it have an actual describable body, it was only until it learned about many actual universes that he actually started getting a body. He learned about various heroes, or rather champions who defended their respective worlds, and was right there and then a powerful and limitless shapeshifter.
It uses its dark power to copy appearance of certain champions and make such its own, to trick and deceive others. Exe was something that can only be described as pure evil, this is because it had a monstrous personality: It thought that everything belonged to it and it alone, and as such it gained a childish attitude thinking all intelligent creatures in many worlds, human or otherwise, were to be its mere playthings for all eternity.
Exe wanted his own world to rule so its "slaves" would have a place to be in so it could enslave them, so it created a patchwork world in a darker image of many popular planets, albeit with some of its own added touches to it. The entity had power to alter the very reality of this nightmarish world, so it's safe to assume that it is in fact a god in its own universe.
Unfortunately, as omnipotent as this creature was, it didn't have any power to leave its world and enter another so it could collect its "toys", but it did manage to have some sort of influence over those with some form of evil in their hearts, and as such the creature was able to get someone (without them knowing) to create a doorway that would bridge the gap between its world and another. This doorway took the form of a computer game, an EXE file, which was burnt into a CD disc. The Game itself, when played, usually shows the inside of the powerful entity's evil dimension and the creature itself manipulates what goes on inside the game to show what it's capable of. When the game's installed onto a computer, Exe has full control of the hard-drive and everything in it, and eventually when the time's right, it'll come out of the game itself to grab its victims and pull them into its world where it can turn them into its slaves. It can only come out to capture such victims because it has very short time being in the outside world, because it doesn't truly belong in any real world.
The entity has never really killed anyone, strangely. Whenever the entity attacks its victims, it only goes for their soul and makes the body look like the person killed themselves, though not always, as for the soul itself captured, for some reason, Exe creates a body for such and puts the soul in it, making the person he stole its own little slave.
The way the creature makes slaves is interesting, because when it captures a person's soul he turns it into a character from another universe that the victim favoured the most: His victims would mainly take the personas of such characters and probably eventually even lose sight of their original personalities. Exe mostly goes after video-gamers and fans alike but he has a certain hunger for the kind of video gamers who talk smack about certain franchises.
As stated earlier, the entity has never "killed" anyone, but it does butcher and torment its slaves in grisly inhumane manners that it leaves people to wonder if it made his eternal slaves immortal too. However, when it does kill someone, it's probably the most horrific thing anyone would or could ever see it do, and have a remote chance of living to tell the tale.
It only kills those it's ultimately bored with, and if it does ever get bored, it turns its own mouth into a black hole and sucks the slave/victim's very existence up. That person who gets eaten by the creature this way is forever gone, never to exist.
Eventually word started to spread about the game disk which contained the doorway into the creature's world, and people started to call it "Sonic . EXE " after the frightening game itself. And eventually the creature itself began to call itself by that or just "Exe", thinking that it's a very simple and fitting name for itself.
As a creature that doesn't exist in our world, Exe seems to dislike both our God and Satan, if such even exist, seeing them both as unfit masters of the "toys" it's collecting, which would very much explain the Sega 666 in the title screen: Exe's way of insulting both deities as well as all those that worship either.
As for his common phrase: "I AM GOD", it only says that because it is in fact a god within its own dark realm, and this fact shouldn't be brushed off or overlooked.
Even though very much enjoys doing its routine in tormenting people who play itss game and then sucking them into its world to be its puppets and slaves, Exe secretly feels that it's not enough, wishing to have full access into our world. The entity hopes that one day, the doorway between its world and ours would break open, and all of its dark forces and powers will pour out into our world.
Maybe someday, it'll get that chance...