Bastet is fairly unique among System Lords, as the legends she inspired on Earth paint her as being a kind and benevolent figure, associated with protecting the homestead, women and children. This probably stems from the fact that all of Bastet's servants and Jaffa warriors are female. Before the discovery of Earth and the Tauri, Bastet did not possess an Unas host, but instead preferred the feline race known as the Sekhmet. Most of her servants and armed forces were also of this race during this time.
In ancient times, Bastet was a minor servant of Ra. She gained her fame and power during Ra's confrontation with Anubis. During a decisive battle, Ra's forces were on the brink of collapse when they were unexpectedly reinforced by a second fleet, which had been gathered together by Bastet. It is universally recognized that Bastet's intervention saved Ra from defeat and death. Ra rewarded her with much wealth and power, and Bastet soon declared herself a System Lord.
She suffered a severe setback, however, during the Second Goa'uld Dynasty, when the upstart Sokar seized most of her territory by force. Bastet survived by making a strong alliance with Kali, which allowed her to recover much of her strength by the Third Goa'uld Dynasty. This alliance has become one of the strongest among any Goa'uld; an attack on Kali is an attack on Bastet, and vice versa. (RPG: "Living Gods: Stargate System Lords")
At some point, she and Kali together made a treaty with the Goa'uld Sobek. Then, at the celebratory feast, they moved against him. Rumor has it that Sobek's head still decorates Bastet's palace in Bubastis.