Blon Fel-Fotch Passameer-Day Slitheen

Blon Fel-Fotch Passameer-Day Slitheen was a member of the criminal Raxacoricofallapatorian Slitheen family who took the skin of the Human MI5 member Margaret Blaine when her family attempted to trigger a nuclear war on Earth, in order to devastate the planet and sell the radioactive remains as starship fuel. (DW: World War Three)

Blon escaped the destruction of 10 Downing Street by using an emergency teleport which only carried one so she was unable to save anyone else in her family. The teleport ended her up on the Isle of Dogs and she later became mayor of Cardiff, beginning the Blaidd Drwg nuclear power plant project above the Cardiff rift to destroy Earth, not to sell as fuel, but with the purpose of using a tribophysical waveform macro-kinetic extrapolator to "surf" into space.

In the process of attempting this she forced open a panel of the TARDIS and gazed into the Heart of the TARDIS and 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. (DW: Boom Town, Bad Wolf)

Behind The Scenes
Early scripts for The Stolen Earth included Blon as an infant making a minor appearance at the Shadow Proclamation.