She was designed by Warren Mears, who also built the Aprilbot, to be physically identical to the Slayer Buffy Summers. She was created to serve as a personal sex slave for the vampire Spike, jealous of the real Buffy's affections for another. Her manner of speech was more supernaturally perky than it was robotic.
Buffybot was later called to fill her doppleganger's duties after it was believed that Buffy had died. While immensely strong in her own right, she was ultimately destroyed by a gang of demonic bikers. She was apparently an inferior fighter to the real Slayer, who violently avenged her twin upon her return.
In the comic book reboot of the series, a new Buffybot is made by Andrew Wells to house the memories of the real Buffy while the body of the real Buffy led another life elsewhere.