The Tosa Inu was bred in Japan on the island of Shikoku and named after Tosa Province, today known as Kochi Prefecture. (These dogs were once known as Japanese Fighting Dogs or Japanese Mastiffs.) The Tosa Inu originated after a number of decades of crossbreeding between native Shikoku fighting dogs and imported Mastiffs, Great Danes, Bulldogs and Bull Terriers and in some parts of the world, the Tosa Inu is classified as a dangerous dog.