Lady Cassandra O'Brien.Δ17

"Moisturise me, moisturise me!"

- Cassandra to her assistants.

Lady Cassandra O'Brien.Δ17 (or better known as Lady Cassandra) is the recurring antagonist in the TV series, Doctor Who. She appears in the episodes The End of the World and New Earth. She claims to be the last pure human, but due to lots of surgeries she is now only skin with a face that is stretched in a frame.

She was portrayed by Zoë Wanamaker.

History
She was born in Texas and her mother was from the Artic Desert. After she moved to England, she had married several times and extended her life through many surgeries, until she was nothing more than a sheet of skin stretched in a frame.

Sabotage on Platform 1
At the destruction of the Earth, Cassandra was on Platform 1 and used Robot Spiders to sabotage the sun filter, take the other visitors like the Ninth Doctor, Rose Tyler, the Face of Boe and many others hostage to get ransom money for more surgery. The Doctor was able to stop her and after her assistants who had to moisturize her disappeared, her body dried and she exploded.

On New Earth
As her brain had survived, she was revived by getting a new piece of skin from the back of her old body and having her eyes being retrieved from a bin. 23 years after the Platform One incident, Cassandra resides in the basement of a hospital on New Earth ran by the Sisters of Plenitude where she had her clone servant Chip lure Rose to her and use a psychograft to transfer her mind into Rose's body. Eventually, she started to work together with the Tenth Doctor, as she wanted to survive and would switch from Rose to the Doctor and at one point, an infected patient. Eventually, Chip offers his body to her which she accepts but unfortunately due to being a clone, Chip has only a short life span, so Cassandra finally accepts death, but not before the Doctor and Rose take her (still in Chip's body) back to see her younger self whose arms she dies in.

Personality
Cassandra (who was probably a tyrannical aristocrat) was very elitist and discriminatory, so she "looked down her nose" at the working-class Rose Tyler, who she considered "common". She showed extreme arrogance at times, claiming to be the last "pure human" and considered all others to be "mongrels" due to their intermingling with other species. She was also very callous, cocky, devious, apathetic, obliquitous, materialistic, tightfisted, arrogant, penurious, manipulative, egocentric, pompous, and evil, being perfectly willing to let all residents of Platform 1 be burned to death by the sun just to make money.

Cassandra's greatest failing was undoubtedly her complete unwillingness to accept death, despite the fact that, according to Rose, it was better to die than live like her. The Tenth Doctor was appalled by her willingness to possess bodies just to prolong her own lifespan, as it robbed the people of their own lives. Only when she discovered that Chip's body was close to death did she finally accept that it was time to die.

Trivia

 * According to the reference book, Doctor Who: Monsters and Villains, which is not a valid source for in-universe articles, Cassandra was born as Brian Edward Cobbs, in the ruins of the Walsall Apology, in the old Calendar Year of 4.99/4763/A/15.
 * In The End of the World, Cassandra talks about "the time when she was a little boy", making her the first openly transgender character in Doctor Who. Despite this fact, in the episode "New Earth", she acted surprised to be in a male body (the Tenth Doctor's), though this might have been because of the writer's forgetting about her originally being a man or perhaps that it had been so long since she her transition that she had forgotten what inhabiting a male body felt like.