Alistair Gordon Lethbridge-Stewart, fully Brigadier Sir Alistair Gordon Lethbridge-Stewart, generally referred to simply as the Brigadier, is a fictional character in the British science fiction television series Doctor Who, created by writers Mervyn Haisman and Henry Lincoln and played by Nicholas Courtney.

Nearly 20 years later, Courtney reprised the role in the DVD Special Feature called "Liberty Hall" in 2009 written by Karen Davies and directed by Brendan Sheppard in which the Brigadier was interviewed by a Times journalist.

That year, Doctor Who later paid tribute to Courtney by announcing the Brigadier had died with a line of dialogue in "The Wedding of River Song".

Later still, a Cyberman avatar of the Brigadier also appears, and achieves some closure with the Twelfth Doctor (Peter Capaldi), in "Death in Heaven" (2014).

He first encounters the Second Doctor in The Web of Fear (1968), when Lethbridge-Stewart is a lieutenant-colonel in the Scots Guards commanding a British Army detachment sent to investigate the Yeti in the London Underground.

When the Doctor was forcibly regenerated and exiled to Earth, Lethbridge-Stewart gave him a position as UNIT's scientific advisor after he helped defeat the Auton invasion.

Other military members of UNIT included Captain Mike Yates, Sergeant Benton and Royal Navy Lieutenant Harry Sullivan.

Called out of retirement to deal with an other-dimensional invasion of armoured knights led by Morgaine, he found himself once again at the Doctor's side.

Sarah Jane asks Lethbridge-Stewart to assist her in accessing UNIT's "Black Archive", a top secret alien artefact facility first alluded to by Douglas Cavendish to Sir Alistair's daughter in Dæmos Rising.

It had been intended by the production team that Lethbridge-Stewart would indeed appear in the story and meet the Tenth Doctor, but Courtney was recovering from a stroke and unable to take part.

In 2009, Courtney reprised the role for a final time in the short film Liberty Hall, an extra for Mawdryn Undead's DVD release.

In the 2017 Christmas special "Twice Upon a Time", the First and Twelfth Doctors unwittingly intervene when Testimony, an organization in the far future that collect memories from those about to die, retrieve a seemingly-innocuous captain in the First World War from the moment before his death, the temporal anomaly of the two Doctors resisting their imminent regenerations disrupting Testimony's efforts to return the captain to his scheduled death.

[10] The Brigadier and the Sixth Doctor were paired in the two-part charity special Dimensions in Time and the Big Finish audio play, The Spectre of Lanyon Moor.

The spin-off UNIT videos Downtime and Dæmos Rising feature Kate Lethbridge-Stewart, the Brigadier's daughter from his marriage to his first wife, Fiona (first named in the Missing Adventure The Scales of Injustice by Gary Russell).

This was first hinted at in Ben Aaronovitch's novelisation of his 1988 serial Remembrance of the Daleks, which featured quotes from a fictional history of UNIT (The Zen Military) written by a Kadiatu Lethbridge-Stewart (Mariatu's granddaughter) in 2006.

In the 1992 New Adventures novel Transit (also by Aaronovitch, and set in the 22nd Century), the Seventh Doctor meets the adopted daughter of General Yembe Lethbridge-Stewart, one of Mariatu's descendants.

The Past Doctor Adventures novel The Wages of Sin by David A. McIntee established that the Brigadier had an ancestor named Alastair Lethbridge-Stewart who worked for the British Government in 1916.

In the novels, Lethbridge-Stewart emerged from retirement again during the events of The Dying Days where he dealt with an invasion of Ice Warriors from Mars in 1997.

The rejuvenated Lethbridge-Stewart, widowed as a result of an accident at sea but back with the military, next appeared in the BBC Books Eighth Doctor Adventures novel The Shadows of Avalon, also by Cornell, where he still held the rank of General but preferred to be called "the Brigadier".

At the conclusion of Sympathy, the alternate Brigadier- referred to as 'Alistair'- joins Warner's Doctor as his companion, but after an unspecified amount of time travelling together, they part ways in the later audio Masters of War, when the two arrive on Skaro and force the Daleks and the Thals to join forces to fight off an invasion by a race known as the Quatch, Alistair remaining once the Quatch are defeated to help the two sides maintain their new truce.

In The Legacy of Time, a special six-part audio to celebrate Big Finish's twentieth anniversary of producing Doctor Who-related audios, the story The Sacrifice of Jo Grant sees Jo Grant and Kate Stewart of the present day being sent back to the 1970s by a series of temporal rifts, where they meet the Third Doctor as he investigates the anomalies in his time.

While Kate attempts to avoid introducing herself to limit the risk of a paradox, the Doctor realizes her identity and convinces her to call her father, introducing herself as the commander of UNIT in the future without identifying herself by name, with the Brigadier (voiced by Jon Culshaw once again) telling her that he is assured that the future of UNIT is in good hands.

The character also appears briefly in a cameo role at the end of writer Paul Cornell's novelisation of the 1997 ITV science-fiction serial The Uninvited.

A character named "Brigadier Lethbridge-Stewart" had earlier appeared in three panels of Uncanny X-Men #218, supervising the arrest of the Juggernaut in Edinburgh, where he also calls out to a "Sergeant-Major Benton" at one point.

The Sherlock Holmes novel Waters of Death by Kel Richards features a naval commander called Ralph Lethbridge-Stewart, alongside Captain Harry Sullivan and Lieutenant Philip Benton.

Although unnamed, two characters strongly resembling Lethbridge-Stewart and Sergeant Benton (who was specifically named) appear in the John M. Ford Star Trek novel How Much for Just the Planet?

The Brigadier briefly appears in Kim Newman and Eugene Byrne's Back in the USSA, supporting Britain's involvement in an alternate Vietnam War.