Overlord

Overlord (オーバーロード, Ōbārōdo) is a light novel series written by Kugane Maruyama and illustrated by so-bin. In the year 2126, a Dive Massively Multiplayer Online Role Playing Game or DMMORPG called Yggdrasil was released, standing out among all other DMMORPGs due to its unusually high ability for the player to interact with the game. After an intense twelve year run the game servers are about to be shut down. Within the game exists a guild, Ainz Ooal Gown, once consisting of 41 members and credited as one of the strongest guilds in the game. Now only 4 of the members remain, the other 37 having quit the game, and only one, an elder lich character named Momonga, continues to play as the guild leader, maintaining their headquarters in The Great Tomb of Nazarick. In the minutes before the shutdown he invites the remaining guild members, but of those only one appears and only for a short while before leaving. While saddened by this, he accepts the reality that his friends have their other lives to take care of and decides to stay logged in until the servers shut down.

When the shut-down time arrives, Momonga finds that the game hasn't vanished; instead, it appears as if Yggdrasil has been recreated as its own reality along with its various NPCs having been brought to life. Momonga has been trapped in the form of his game avatar, leaving him unable to use the normal player functions such as General Message, or even to log out. With no other option, Momonga sets out to learn if anyone from the real world is also in this new world with him. Taking on the name of Ainz Ooal Gown, a message to any other players, Momonga begins exploring the world in an attempt to figure out what has happened while searching for anyone or anything that could help him solve this mystery, while ensuring the safety of Nazarick. Ainz Ooal Gown seems to have modifications made to his behavior by in-game mechanics, because he demonstrates no moral qualms with killing and other actions that are taboo in the real world. This is a story about the psychology of a creature beyond ethical concerns with near-limitless power.

See here for more characters coming from this universe.