Monster Rancher, known in Japan as Monster Farm (モンスターファーム, Monsutā Fāmu?), is a series of life simulation role-playing video games created by Tecmo (now Tecmo Koei). The series currently consists of fourteen games across different video game platforms, and future titles are planned. In addition, the series has been adapted into an anime.
The renaming of the franchise was probably done to avoid confusion with the short lived Saban series Monster Farm, which aired around the same time as the Monster Rancher anime.
Read more about Monster Rancher: Story, Games, Anime, Reception