Zygon Osgood

"Petronella Osgood" was a Zygon who kept the human Osgood's form as part of Operation Double. Following her death, Bonnie took her place.

Becoming Osgood
A group of Zygons landed on Earth in 1562 and retreated into a stasis cube until 2013. Upon leaving the stasis cube, by then housed at the Under Gallery, one Zygon took on the form of Petronella Osgood after ambushing the real one and taking her inhaler. She escaped, however, and reclaimed her inhaler while doing so. (TV: The Day of the Doctor) The Zygon decided not to kill her in order to maintain access to her wealth of knowledge. (PROSE: The Day of the Doctor)

Later, three incarnations of the Doctor erased the memories of both the humans and their Zygon counterparts when they took control of the UNIT Black Archive, forcing the two species to negotiate a ceasefire. When the Zygon Osgood suffered an asthma attack, the real Osgood quietly passed over her inhaler, allowing these two to secretly know which was human and which was Zygon. (TV: The Day of the Doctor)

Operation Double
The two Osgoods then created Operation Double, where a group of 20 million Zygons would be allowed to live on Earth and take on the form of the nearest person they could find. The treaty could only be maintained if both humans and Zygons agreed to live among each other in peace, and that no harm would come to anyone. They were given a device called the Osgood Box by the Doctor, to be used only in a dire emergency. (TV: The Zygon Invasion)

In 2014, one of the Osgoods was sent to Bonnybridge to investigate another U.F.O. sighting in the area. Because of this, she missed the first known interaction between the Twelfth Doctor and UNIT as well as the Fractures' attack on London. (COMIC: The Fractures)

Death
After began to deploy her Cyberman army across the world, (TV: Death in Heaven) the Zygon Osgood (AUDIO: Narcissus; WC: The Zygon Isolation) confronted and secured her. She was stationed near Missy during her captivity aboard Boat One, who told Osgood she was planning on killing her. Missy proceeded to count down to Osgood's death, taunting her with each number. She then unlocked her handcuffs, killed her guards and grabbed hold of Osgood. Despite claiming to be more useful to Missy alive, Osgood was vaporised, with only her glasses remaining intact until Missy crushed them under her heel. (TV: Death in Heaven)

Legacy
After an encounter with the Twelfth Doctor, another Zygon, Bonnie, decided to become an Osgood, taking the place of the one who had died. Neither Osgood would reveal if they were human or Zygon. (TV: The Zygon Inversion)

Osgood Zygon