Video Kate Lethbridge-Stewart first appears in the direct-to-video spin-off
Downtime (1995), in which Kate is depicted as having grown up not knowing of her father
Brigadier Lethbridge-Stewart's work fighting extraterrestrial threats in the
Unified Intelligence Taskforce (UNIT) and believing he had a more ordinary military job. Blaming his work for the disintegration of their family, she becomes estranged from him and lives on a
narrowboat with her only son, Gordon. However, a shared experience fighting the
Great Intelligence alongside the Brigadier and
Sarah Jane Smith allows her to reconnect with her father and develop a closer relationship. Later, Kate battles a Dæmon alongside ex-UNIT operative Douglas Cavendish in the direct-to-video spin-off
Dæmos Rising (2004). In "
The Day of the Doctor" (2013), Kate and UNIT's scientific advisor
Petronella Osgood encounter the Eleventh Doctor again alongside his earlier incarnations, the
War Doctor and the
Tenth Doctor. They confront shape-shifting
Zygons in the Black Archive, UNIT's secret vault in the
Tower of London, and negotiate a peace treaty allowing 20 million Zygons to settle on Earth disguised as humans. Kate works alongside the
Twelfth Doctor for the first time in "
Death in Heaven" (2014). When
Cybermen are released onto the streets by
Missy, Kate and Osgood arrive with UNIT officers and take Missy and the Doctor into custody on the plane Boat One. However, Missy escapes when Cybermen attack Boat One, during which a part of the fuselage blows off and Kate is sucked out of the plane. She is saved and returned safely to the ground by her father, who was converted into a Cyberman. Later, Kate summons
Clara Oswald to UNIT headquarters in "
The Magician's Apprentice" (2015) when Missy freezes all planes on Earth, which turns out to be her way to get UNIT's attention to arrange a meeting with Clara. In "
The Zygon Invasion" / "
The Zygon Inversion" (2015), Kate goes to
Truth or Consequences, New Mexico to investigate a splinter group of Zygons who start an uprising after rejecting the peace treaty made with humans. Surviving an attack by a Zygon rebel, she takes its place and reconvenes with the Doctor in the Black Archive. A standoff ensues there between her and the Zygon rebel leader Bonnie with two Osgood Boxes that could unmask or destroy every Zygon on the planet. Aided by the Doctor, the conflict ends with both sides re-affirming the peace treaty. Kate re-appears in "
Survivors of the Flux" (2021), which reveals that an alien by the name of the Grand Serpent infiltrated UNIT over several decades and facilitates its shutdown in 2017. When Kate threatens to expose him, she is forced to go on the run after a failed attempt on her life. During the 2021
Sontaran invasion of Earth in "
The Vanquishers" (2021), Kate emerges to lead the human resistance and triumphs with the help of the
Thirteenth Doctor. By 2022, Kate is able to re-establish UNIT. She takes the Master into custody in "
The Power of the Doctor" (2022), but UNIT's headquarters are overrun by Cybermen and blown up. Kate attends a companion support group meeting and discusses recruiting them to UNIT. Kate begins using her full surname Lethbridge-Stewart again and has become the
commander-in-chief of UNIT by the time she meets the
Fourteenth Doctor in "
The Giggle" (2023). Together, they face and defeat
the Toymaker, a battle which causes the Doctor to
bi-generate into the
Fifteenth Doctor. During an alternate timeline shown in "
73 Yards" (2024),
Ruby Sunday goes to Kate for help regarding a mysterious woman following her and causing all others who approach the woman to flee; in her attempt to capture the woman, Kate befalls the same fate and abandons Ruby. In "
The Legend of Ruby Sunday" / "
Empire of Death" (2024), the Fifteenth Doctor and Ruby come to UNIT for help regarding the mysteries of Ruby's mother and the recurring face of Susan Triad, whom they discover is actually the harbinger of the god of death,
Sutekh. Sutekh destroys all life on Earth, killing everyone including Kate, but she is brought back to life after his defeat by the Doctor. In "
Lucky Day" (2025), Ruby's new boyfriend Conrad Clark turns out to be using her in pursuit of his agenda of turning the public against UNIT. Following the appearance of creatures called Shreek supposedly hunting Conrad, Ruby calls Kate for help, who arrives with UNIT soldiers to stop the creatures. However, they are revealed to be fake while Conrad livestreams the encounter, a setup orchestrated by him to spread a conspiracy theory claiming the non-existence of aliens and fraud by UNIT. As a result, Kate has to deal with growing distrust by the British public as media coverage turns against the organization. Conrad infiltrates UNIT's headquarters with a gun and a camera live-streaming to his social media to demand Kate admit to his conspiracy. She reacts by releasing the real Shreek upon Conrad and refusing to help him until he admits on air that he was lying for personal gain. Although UNIT is saved as a result, there is some concern about Kate's willingness to cross the line and the potential consequences of her actions which she brushes off. "
Wish World" / "
The Reality War" depicts an altered reality created by
the Rani and overseen by Conrad in which Kate serves as the head of the Unified
National Insurance Team. The Doctor and
Anita Benn, an employee at the Time Hotel, use the hotel's doors to restore the true memories of everyone at UNIT headquarters, who then send signals to microchips installed in every UNIT employee in London to break them out of the illusion as well. The Rani unleashes creatures called Bone Beasts on UNIT, leaving Kate and UNIT to defend themselves, before the Doctor restores reality back to normal.
Audio drama Beginning in 2015, Jemma Redgrave reprised the role of Kate for the ongoing
Big Finish Productions audio drama series
UNIT, which marked the company's first major release featuring characters from the revived
Doctor Who series. The series also starred
Ingrid Oliver as Petronella Osgood, who appeared on television as UNIT's scientific advisor. The first four-part boxset of the series,
Extinction, saw the team confront an alien invasion by the Nestene Consciousness's army of plastic
Autons. Kate crossed over with Big Finish's main line of
Doctor Who audio dramas on two special occasions. The first was in
The Sacrifice of Jo Grant, the third part of the boxset
The Legacy of Time celebrating the company's 20th anniversary, which featured Kate traveling back in time to the classic UNIT era and meeting the
Third Doctor and
Jo Grant, played by Tim Treolar and
Katy Manning respectively. She also appeared in the audio drama
Past Lives, the first of a seven-part series produced for the programme' 60th anniversary entitled
Once and Future, in which Redgrave starred opposite
Tom Baker as
Fourth Doctor,
Sadie Miller as
Sarah Jane Smith, and
Rufus Hound as
the Monk. ==Development==