Cassandra was portrayed by Zoë Wanamaker.
According to Cassandra, her father, a Texan, and her mother, who came from the Arctic Desert, were the last to be buried in Earth's soil. She was born a male on Earth and lived on the edge of the "Los Angeles Crevasse". At some point, she was biologically altered into a female through advanced genetic engineering. She was married several times. Her life was extended through a series of seven hundred and eight plastic surgery operations, until she was nothing but a piece of skin stretched onto a frame with eyes and a mouth, connected to a brain in a jar below. The skin had to be constantly moisturised to keep it from drying out.
End Of The WorldEdit
In the episode "The End of the World", Cassandra attended the Earth Death event aboard Platform One. However, she wasn't interested in mingling. Cassandra had plotted to sabotage the station and engineer a hostage situation with herself as one of the victims, using the Adherents of the Repeated Meme androids to draw attention away from herself and collect a fortune in ransom money so that she could fund further surgeries to keep herself alive.
When that plan was exposed by the Ninth Doctor, she teleported off the station, leaving the space station to be consumed by the expanding Sun — eliminating both the evidence and allowing the shares she held in the guests' rival companies to triple.
However, the Doctor reset Platform One's systems, saving the station, and also reversed the teleportation feed, bringing Cassandra back. In the heat, and without her assistants to moisturise her, Cassandra's skin dried, stretched and exploded, apparently killing her, although her brain survived.
Twenty-three years later, Cassandra was living on New Earth. Her brain had survived, her eyes had been retrieved "from the bin" and she was "repaired" with extra skin taken from the back of her previous body. She hid in the basement of the hospital run by the Sisters of Plenitude, and was tended to by Chip, a force-grown clone bred to be her servant.
When she discovered Rose and the Tenth Doctor were on New Earth, she lured Rose to her hiding spot in the basement of the hospital and used a psychograft to transfer her consciousness into Rose, taking control of her body.
This was in part to gain revenge on Rose and also to further her lifespan, intending to use Rose's body to live on for centuries. Her impersonation of Rose was marred by her Sloane accent, poor imitation of rhyming slang, and anachronistic technical knowledge. In the end, however, it was her lack of compassion that gave her away. Her first instinct upon learning of the Sisters' "plague farm" was to blackmail them; when this failed, she released the clones, who in turn, released more of them.
Using the lift's disinfectant, Cassandra helped the Doctor cure the clones with the Doctor jubilantly telling Cassandra she couldn't deny the new humans as she helped create them. The Doctor demanded Cassandra to leave Rose's body. Chip appeared and Cassandra saw a new body to inhabit. Chip openly volunteered Cassandra to inhabit his body. After Cassandra took over Chip's body, she realised his body was dying; though the Doctor offered to help save her, Cassandra finally accepted her death.
As a final request, the Doctor took her back in time to the party where she had been told she was beautiful. In Chip's body, Cassandra told her past self she was beautiful, before dying in her past self's arms.