Queen mother of all Tok'ra symbiotes, believed to have been destroyed by the Supreme System Lord Ra some 2,000 years ago. Egeria's last whereabouts were on the world of Pangar, once occupied by Ra's army as a base of operations. Here, Egeria fought Ra, and legend says he destroyed her. However, Pangaran tomb texts described her as buried alive. It was later discovered the Pangarans had located her stasis jar and, for 50 years, experimented on her and her offspring.
Realizing what they had done, the Pangarans released Egeria, albeit unexpectedly, where she took the host body of Kelmaa to communicate with Dollen. Egeria had been poisoning her young, making them essentially vegetables, because she believed once the Pangarans had discovered the flaws in the experiments, they would give up. This is not what happened, and consequently derived a substance from her offspring that became tretonin.
Egeria, finally free, discovered what the Tok'ra had become after thousands of years, and as her last act, saved the Pangarans from the inbred defect, restoring them all to health. She died shortly thereafter. Her remains were taken back with the Tok'ra.
Crossroads - The Tok'ra Anise tells SG-1 of Egeria and the birth of the rebel movement, and the tale of her alleged death.
Cure - SG-1 learns the Pangarans have been harboring Egeria, running experiments on the symbiote to discover it's rehabilitative attributes.