The animation studio that preceded Studio Ghibli was Topcraft.
Topcraft was a Japanese animation studio founded in Tokyo on February 1, 1972, by former Toei Animation producer Tōru Hara. It became known internationally through hand-drawn projects made with Rankin/Bass, including The Hobbit in 1977, The Return of the King in 1980, and The Last Unicorn in 1982. This earlier work gave Topcraft substantial experience in detailed fantasy animation.
The studio’s most important connection to Ghibli came through Nausicaä of the Valley of the Wind, directed by Hayao Miyazaki and released in 1984. Nausicaä was produced at Topcraft, with Hara involved in the studio’s operations. After Topcraft encountered financial difficulties and dissolved in 1985, Miyazaki, Isao Takahata, and producer Toshio Suzuki acquired its assets and established Studio Ghibli on June 15, 1985.
That history explains why Nausicaä is often discussed alongside Studio Ghibli films even though it predates the studio’s founding. Topcraft was not merely an unrelated predecessor: much of the talent and production experience carried directly into Ghibli. Production I.G., Madhouse, and Toei are all important Japanese animation companies, but none is the canonical predecessor in this context.