Megami Tensei (lit. Reincarnation of the Goddess) refers to a franchise of games developed and published by Atlus beginning in 1987 with the release of Digital Devil Story: Megami Tensei. The series is comprised of several branches each with their own themes, styles and gameplay mechanics. Nearly each game in the franchise is a stand alone narrative; yet each game is linked by common elements such as theological themes and the unique press turn battle system.
The series is quite popular in Japan and has a cult following in the west (save for Persona 5, by far the most commercially successful entry), and has spawned many film and literary adaptations including numerous anime, manga and even a live action adaptation of Devil Summoner.
Megami Tensei finds its roots in a science-fantasy trilogy of novels written by Aya Nishitani. The Digital Devil Story novels follow the story of Akemi Nakajima, a highschool student who develops a computer program capable of summoning demons in order to get revenge on his bullies. Eventually however, the demons get out of hand and Nakajima, with the help of Yumiko Shirasagi (the reincarnation of Izanami, hence the game title), must embark on a journey to defeat Lucifer and his generals.
The novels were very popular in Japan and thus the books received an OVA adaptation alongside a video game tie-in– what would become the first Megami Tensei game: Digital Devil Story. Once it was decided to adapt the books to a game, the pitch was given to Nintendo who ended up turning it down due to the mature content of the novels. Eventually, the project fell into the hands of Atlus who ended up publishing the game through Namco (now Bandai Namco) on September 11, 1987. The game received successful sales and was praised by critics for its revolutionary demon recruitment system and unique cyberpunk atmosphere, garnering a 31/40 from Famitsu.