Cassandra
Cassandra has appeared twice in Doctor Who in Series 1 : Episode 2 (The End of the World) alongside the Ninth Doctor and again in Series 2 : Episode 1 (New Earth) alongside the Tenth Doctor. Cassandra’s described herself as the last “pure human” after humans had begun to interbreed with other intelligence life forms, or altered themselves to the point that they didn’t call themselves human anymore. Cassandra herself was only a piece of skin, stretched over a frame work with her brain in a designer jar of preserving fluid beneath her, over the course of 708 plastic surgery operations. In this state, Cassandra required two assistants to keep her skin moisturised. Rose referred to her as “Michael Jackson” and the two did not get along on board Platform One. During the episode The End of the World, Cassandra used robotic spiders to sabotage Platform One’s computer systems and resulting in the sun shields protecting the inhabitants from the resultant expansion of the sun and androids calls the Adherents of the Repeated Meme. Cassandra used the androids in an attempt to divert attention from herself as the culprit of the crimes. However, when the Doctor caught her, she simply teleported off to her own ship and left Platform One to be destroyed by the sun flare destined to destroy the sun. After saving Platform One, the Doctor reversed the teleport and Cassandra returned without her moisturising assistants. With the increased heat and lack of moisture, Cassandra’s skin stretched, cracked and ruptured, though her brain was not seen to be destroyed.
When we next see Cassandra in Series 2, she has had a new skin graft from the back of her old body, and is being tended to by a forced-growth clone named Chip. Cassandra and Chip are hiding in the basement of the hospital run by the Sisters of Plenitude on New Earth. She finds the Tenth Doctor and Rose in the hospital and forces the lifts to take Rose to her in the basement. With Rose captive, Cassandra uses a psychograft to transfer her consciousness into Rose’s body. This was done for three reasons, to find out what the Sisters of Plenitude were hiding, to return to a body of pure human stock and to also gain revenge on the Doctor and Rose. While investigating the clones built by the Sisters with the Doctor, she decides to try and blackmail the Sisters and knocks the Doctor out. Cassandra also releases all of the cloned humans resulting in Rose, Chip and the Doctor fleeing to the basement, where Cassandra then swaps consciousness between Rose, the Doctor and one of the cloned humans. In the end however, Cassandra assists the Doctor in curing the cloned humans and moves into Chip’s body (who willingly invited her in). Chip’s body however begins to die and Cassandra accepts that it is also time for her to die. Before she does, the Doctor takes her back in time to meet her younger self when she still had a body. In Chip’s body, Cassandra complements her younger self before dying in the younger Cassandra’s arms.