"25 years ago today I had the honor to introduce the world to my version of Buffy Anne Summers," Gellar wrote on Instagram. "It was an uphill battle. A mid season replacement, on a new network based on a movie, that was by no means a giant success. But then there was you. The fans. You believed in us. You made this happen. You are the reason 25 years later we are still celebrating. So today we celebrate you as well." ALSO: Buffy finds a new cable home on Fuse, starting Oct. 1.