Megami Tensei

Megami Tensei is a Japanese Game Series created by Aya Nishitani, Kouji "Cozy" Okada, Ginichiro Suzuki, and Kazunari Suzuki. Developed and published by ATLUS under ownership of SEGA, the franchise consists of multiple subseries and covers multiple Role-Playing Game genres including tactical role-playing, Action Game, and Massively Multiplayer Online Role-Playing Game.

The game series was originally based on the Science Fiction novel "Digital Devil Story" by Aya Nishitani, with later entries having their own stories, characters, plot themes shaped by the player's in-game choices, and the ability to recruit creatures (e.g. demons, Personas) as an aid. Elements of philosophy, religion, occultism, and science fiction have all been incorporated into the series at different times.

Source: Wikipedia (edited)