Origins
Satoru Suzuki was once just an average Japanese salaryman, that spent most of his money and time in a game called Yggdrasil, a DMMO-RPG (Dive Massively Multiplayer Online Role Playing Game). Basically, a game where you connect your brain to a machine and can play it with the body of your avatar as if the game was real.
In this game, Suzuki’s character was Momonga, an undead magic caster skeleton. He was a level 100 player, from one of the most powerful guilds in the world. He didn’t have any friends in real life, so, he treated the other players of his guild as if they were his family.
After several years playing, his friends slowly stopped logging in, and the game was going to end. Momonga was the last person of his guild still active.
But, somehow, when the game was about to be shut down, his guild was transported to a fantasy world that was apparently real. All the NPCs created personalities and started treating Momonga as their god.
Since then, he’s trying to find other players in this new world and changed his name to Ainz Ooal Gown, the name of his guild.
Creation
Momonga is the protagonist of the series Overlord, which started as a Web Novel, written by Kugane Maruyama, but later was released as a Light Novel.
There are also anime and manga adaptations of the story.