Blon Fel-Fotch Passameer-Day Slitheen

Blon Fel-Fotch Passameer-Day Slitheen was a female Raxacoricofallapatorian and a member of the criminal Slitheen family. On Earth, she took the skin of the human MI5 member Margaret Blaine.

Regressed to an egg by the Heart of the TARDIS, she began a new life as Margaret Ag-Kris Therur-Ford Jingatheen.

Upbringing
According to the story Blon told the Ninth Doctor, when she was thirteen she took part in her first hunt and knew that if she refused to join her family's criminal activities, she would undergo unpleasant ritual execution with Venom Grubs at the hands of her father. (TV: Boom Town)

Criminal career
By March 2006, the Slitheen family had killed Margaret Blaine so that Blon Fel-Fotch Passamer-Day could wear her skin. (TV: Aliens of London) The Ninth Doctor believed she had done it personally. (TV: Boom Town)

She went along with her family's plan to trigger a nuclear war on Earth, in order to devastate the planet and sell the radioactive remains as starship fuel. (TV: World War Three) She was present at 10 Downing Street with her fellow Slitheen, "Joseph Green" and "Oliver Charles". Green had taken over the government as Acting Prime Minister, which would give the Slitheen more power in Britain. Blaine was present when the Slitheen murdered General R. Asquith, and remained with Green for the rest of the crisis. When Rose Tyler, Harriet Jones and Indra Ganesh discovered the body of the Prime Minister, Blon taunted them and started to kill Indra. (TV: Aliens of London)

Blon hunted down Rose and Harriet, but was distracted by the Doctor when he entered with a fire extinguisher. The Doctor, Rose and Harriet placed themselves safely behind the walls of the Cabinet Room. Thinking they couldn't do anything trapped inside the "box", Blon continued with the plot. She took the skins of fellow Slitheen members who had been summoned to Downing Street and waited for the launch codes to be given to Downing Street. The Doctor contacted Mickey Smith, who launched the missile UGM-84A at Downing Street, killing the Slitheen while the Doctor, Rose and Harriet rode out the explosion inside a small, sturdy cupboard. (TV: World War Three)

Blon escaped the destruction of Downing Street by using an emergency teleport which could only carry one. The teleport landed her in a skip on the Isle of Dogs before arriving in Cardiff, where she managed to get herself elected Lord Mayor of Cardiff. (TV: Boom Town) Her predecessor, Barry Jackson, had killed the former mayor and blamed it on the Auton invasion. (AUDIO: One Rule)

Secretly, Blon planned to take advantage of the space-time rift located there and advocated a plan for a proposed nuclear power plant called Blaidd Drwg. She wanted to cause an "accident" at Blaidd Drwg. This disaster, located so near the rift, would destroy Earth and provide her tribophysical waveform macro-kinetic extrapolator with sufficient power for her to ride the "surf" into space to escape. She knew that failing this, anyone who arrested her would take the extrapolator for themselves, having "considerable technology of their own" and being "captivated" by the extrapolator. The extrapolator was programmed to lock onto the nearest alien power source and open the rift, still allowing her escape.

She killed anyone who questioned her plans, such as Mr Cleaver. However, in a rare act of mercy, she spared the journalist Cathy Salt after hearing the young woman talk about her family, reminding Blon of her own lost relatives. Soon after, the Ninth Doctor and his companions arrived to stop her; Jack Harkness confiscated the extrapolator and used it to refuel the TARDIS quicker. The Doctor remained uncertain as to what do as she had been sentenced to death on her homeworld in absentia; Blon pleaded the Doctor for mercy and clemency. When the extrapolator began opening the rift through the TARDIS, Blon, threatening Rose, demanded Jack to place the extrapolator at her feet. The extrapolator nearly pulled apart the TARDIS, but the heart of the TARDIS was forced open and Blon looked directly into its light; she was regressed backwards along her timeline to the form of an egg. The Doctor returned her to her home planet to be placed with another family. (TV: Boom Town)

Second chance
Renamed Margaret, the former Slitheen was adopted by the Jingatheen family. Left with her human skin suit, Margaret would keep and wear it throughout her life. Eventually, she joined the Shadow Proclamation, under which she worked as a Detective Inspector. Attached to the Judoon rocket Typho, Margaret boarded the Max Capricorn container ship Jeden with the Judoon led by Captain Nibri and came face to face with the Twelfth Doctor. (COMIC: A Confusion of Angels)

As Blon Fel-Fotch Passameer-Day Slitheen
Having been brought up in a criminal family, Blon was fixated on making a profit whatever the cost, going as far as to commit murder. She lacked any form of empathy or morals, and was more than willing to commit terrible actions such as murder in order to further her or her family’s goals.

Blon held particular disdain towards humans, comparing wiping out mankind to “stepping on an ant hill”. She described Earth as a savage and ”godforsaken rock”. (TV: World War Three)

Despite her brutality and killer instinct, Blon proved to be intelligent, calculating, patient and manipulative during her reign as Mayor of Cardiff, having set up a plan to destroy Earth as well as maintaining contingencies. (TV: Boom Town)

However, Blon was capable of rare acts of mercy. But the Doctor simply reduced this to being how Blon lived with herself being a killer, which she reluctantly acknowledged.

As Margaret Ag-Kris Therur-Ford Jingatheen
After having been given a second chance at life, Blon, renamed Margaret, was raised by the Jingatheen family and grew up to become an agent of the Shadow Proclamation. Once she met the Doctor again, she showed courage, bravery and dedication, standing by the Doctor and defending his allies against the Weeping Angels. (COMIC: A Confusion of Angels

Other information
While she served as mayor of Cardiff, Idris Hopper served as her secretary. (TV: Boom Town, PROSE: The Twilight Streets)

Behind the scenes

 * Though, technically, Margaret Blaine has never appeared on Doctor Who, her Slitheen impersonator, Blon Fel-Fotch Passamer-Day Slitheen, gets credited as "Margaret Blaine" in the stories in which she appeared.
 * The infant Blon Fel-Fotch Passamer-Day Slitheen (played by an actor of appropriate size) would have appeared in the Shadow Proclamation in an earlier draft of The Stolen Earth. She would have been taken in by the Jingatheen family and, strangely, would be called Margaret by her father.

 Блон Фэл-Фотч Пассамир-Дэй Сливин