Petronella Osgood

Petronella Osgood was a scientist who worked for UNIT, acting in a capacity of a personal assistant to Kate Stewart, in the early 21st century.

An admirer of the Doctor, she eventually met the Time Lord during the infiltration of UNIT by Zygon invaders, which was resolved by the Eleventh Doctor joined by his tenth and war incarnations. (TV: The Day of the Doctor)

The original Osgood and her Zygon double became indistinguishable from each other to everyone else. They refused to identify which of them was Zygon and which was human. (TV: The Zygon Invasion) One of them was killed by. (TV: Death in Heaven) After a Zygon rebellion was ended peacefully, the Zygon rebel leader Bonnie took on the form of Osgood to maintain the peace. Both Osgoods still refused to identify if she was the human or Zygon version but promised to one day when no one would care anymore. (TV The Zygon Inversion)

Biography
Osgood came from a family of science geeks. (AUDIO: Earthfall) She had a sister. (TV: The Day of the Doctor)

Joining UNIT
Osgood helped stop a Nestene invasion when an army of Autons was created by Simon Devlin's 3D-printers. (AUDIO: Vanguard, Armageddon) Together with Lieutenant Sam Bishop, she was deployed to the Gobi Desert in Mongolia in search of a Nestene energy unit. (AUDIO: Earthfall) She was able to free Captain Josh Carter from Nestene control. (AUDIO: Armageddon)

Meeting the Doctor
She was present when the Eleventh Doctor's TARDIS, along with both the Doctor and Clara Oswald, were brought to HQ in an effort to understand what had happened to several paintings in the Under-Gallery. The Doctor took a liking to her long multi-coloured scarf, which was strikingly similar to one he wore in his fourth incarnation. She displayed a type of hero-worship belief in the Doctor, twice "praying" to him to save her during moments of danger.

On the Doctor's orders, she and fellow scientist McGillop analysed the stone dust in the undergallery under the National Gallery, and it was Osgood who realised the dust was the smashed remains of the statues that had previously occupied the space. She then realised with horror that their places had been taken over by the Zygons that had escaped from the paintings. She was able to escape from them, although she was duplicated by one of their number before she got away.

She was asthmatic, and often forgot to use her inhaler when needed, especially when over-excited, often being reminded by Kate when she started wheezing. The Zygon who took her form disliked this, annoyed at "getting one with a defect," and promptly took her inhaler. When she escaped from this Zygon by tripping it with her scarf, she reclaimed her inhaler. Osgood was in the Black Archive with her Zygon version when Kate threatened to destroy London, rather than let the alien technology in the archive fall into Zygon hands. Like the other humans and Zygons in the room, her memory was temporarily cleared by three incarnations of the Doctor, so that she could not recall whether she was the real Osgood or her Zygon duplicate. As peace talks ensued, she realised who the real Osgood was when the Zygon duplicate began wheezing and did not have the inhaler. She gave it to the Zygon version, and both Osgoods agreed to keep their discovery a secret so as not to disrupt the peace talks. (TV: The Day of the Doctor)

The two Osgoods
The two Osgoods 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, Osgood 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 the Fractures' attack on London. (COMIC: The Fractures)

After began to deploy her Cyberman army across the world, Osgood confronted and secured her. She was stationed near Missy during her captivity aboard Boat One, who told Osgood: "I'm going to kill you in a minute," calling it their "secret girl plan". Missy proceeded to count down to Osgood's death, tormenting her after each number. She then escaped 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. The Twelfth Doctor later discovered them, crushed on the ground, and realised that Missy had murdered her. (TV: Death in Heaven)

After the death of one of the Osgoods, the other one refused to state whether she was the Zygon or the human. She became a target of a revolt from a rogue group of Zygons who believed they had been betrayed. (TV: The Zygon Invasion)

After the Doctor convinced Bonnie, the leader of the Zygon revolt, to stop her plan, Bonnie also assumed Osgood's form and acted as the second protector of Earth alongside the other surviving Osgood. She felt that they were a credit to both humans and Zygons and planned to take on the role of protecting the Earth from threats. (TV: The Zygon Inversion)

Personality
Osgood was a fanatic admirer of the Doctor. She dressed according to his fashion senses from various incarnations, choosing to wear a similar scarf to that worn by the Fourth Doctor. (TV: The Day of the Doctor) She later wore a leather jacket similar to the one worn by the War Doctor, trainers similar to those worn by the Tenth Doctor and a bow-tie similar to that worn by the Eleventh Doctor. She also admitted that "bow-ties are cool" – a phrase often used by the Eleventh Doctor. She also wore a shirt with question marks on the collars, like the Fourth, Fifth and Sixth Doctors, and a cardigan similar to the Seventh Doctor's. (TV: The Zygon Invasion) When asked by the Twelfth Doctor if she would like to travel with him, she was so excited that she had to use her inhaler. (TV: Death in Heaven) Osgood would become sad if she learned she missed a chance to see the Doctor; one of her fellow scientists even stated she would be disheartened to learn the Doctor had regenerated again after she had just started mimicking his previous self's fashion. (COMIC: The Fractures)

Osgood was also very intelligent. She alone was able to work out the reason why the Zygons smashed the statues in the Under-Gallery. (TV: The Day of the Doctor) She also surprised the Doctor by guessing correctly that Missy was the Master regenerated into female form: UNIT kept files on all past Prime Ministers, including the Master. (TV: Death in Heaven) She also could come up with a plan for invading Earth by killing the Doctor, by shooting him between the eyes for each regeneration, never allowing him to talk. (TV: The Zygon Inversion)

She managed to figure out whether she or her Zygon doppelganger was the real Osgood after the Tenth and Eleventh Doctors, joined by the War Doctor, jumbled their minds, making them unable to determine their own species, in an attempt to facilitate negotiation of the ultimate peace treaty. She managed to determine this as her Zygon counterpart suffered an asthma attack, motivating her to pass her asthma inhaler to the other Osgood. (TV: The Day of the Doctor)

Osgood had a sister to whom she negatively compared herself. (TV: The Day of the Doctor) Missy understood that she had little confidence in herself. Osgood was able to keep her cool, even when faced with the threat of death from Missy and tried to reason her way out. (TV: Death in Heaven)

Behind the scenes

 * On 24 July 2014, Ingrid Oliver appeared in character as Osgood in a video thanking fans for helping the official Doctor Who Twitter account reach one million followers.
 * In DWM 484 Steven Moffat admitted his intention when writing was for Osgood to be the daughter of UNIT soldier Tom Osgood. However, he did not want to state this definitively in the script so fans were able to have their own interpretations.
 * Osgood appears as a background character in the London scene and the hidden Black Archives location in the Doctor Who level pack in LEGO Dimensions.