Cassandra was a 12 year old girl when the Goa'uld Nirrti created a disease to destroy everyone on her home planet of Hanka. As the only survivor, she was rescued by SG-1 and brought back to Earth, only to discover that Nirrti had also implanted the means for an artificial mechanism to form and grow within her chest. The mechanism was made of iron and potassium on one side, and naquadah on the other, separated by a layer of fatty tissue that decayed at a regular atomic rate. Designed as a Trojan horse, the device was meant to be triggered by the stargate and would destroy Earth with an intense nuclear reaction, releasing high levels of gamma and particle radiation. Unable to save Cassandra or to surgically remove the device, SG-1 prepared to leave her in an abandoned nuclear facility. However, distance from the stargate reversed the symptoms, and Cassandra survived. The device was neutralized and reabsorbed into her system, although traces of naquadah remain in her blood, enabling her to detect the presence of a Goa'uld.
Afterwards, Cassandra remained on Earth. She was adopted by Dr. Janet Fraiser and became Cassandra Fraiser, born in Toronto and growing up as an average teenager with her very own dog, a gift from O'Neill. At age 16, as she reached puberty, the remnants of another of Nirrti's earlier experiments to create a hok'tar, or advanced human host, activated a dormant retrovirus in Cassandra's system that began to rewrite her DNA and caused a high fever, seizures, and telekinesis. SG-1 was unable to reverse the symptoms, however Nirrti was captured by SG-1 and was forced to cure Cassandra of the virus in exchange for her own freedom.
Cassandra has remained close with all the members of SG-1, especially Carter with whom she used to play chess every other Saturday, and they have taken on the role of her adoptive family and her support. After the death of Janet Fraiser, Carter remained especially close to Cassandra as a parent and role model, and when Cassandra was going through a difficult period, Carter left the SGC for a research and development position at Area 51 that would allow her more flexibility and more time to be available to Cassandra.
When Cassandra was old enough to understand, Carter told her of SG-1's mission to 1969, in which a solar flare accidentally flung them far forward in time, where they were met by Cassandra as an old woman. In a self fulfilling prophecy, Cassandra will be in the gateroom of the future, to send SG-1 back home.
Portrayed by: Katie Stuart, Colleen Rennison, Pamela Perry
Cross Reference: Samantha Carter, Cassandra's Dog, Janet Fraiser, Hanka, Hok'tar, Nirrti, Mrs. Struble, Time Travel 1969, Dr. Warner
Episode Reference: Singularity, In the Line of Duty, 1969, Rite of Passage