Sir Alistair Gordon Lethbridge-Stewart — often called the Brigadier or the Brig — was one of the founders of the United Nations Intelligence Taskforce (later renamed the Unified Intelligence Taskforce).Through his work, he became a trusted ally of the Doctor, as well as a personal friend.(PROSE: The Forgotten Son) He was of Scottish descent.(TV: Terror of the Zygons) Both his grandfather and great-uncle were born in Scotland, as was his father.Working closely with Travers, Lethbridge-Stewart founded and led the Home-Army Fifth Operational Corps for a short period — during which he was promoted to Brigadier — before becoming the commander of UNIT's UK operations.Lethbridge-Stewart grew close to the Doctor's third incarnation in the several years they spent together combating alien incursions during the Doctor's exile on Earth.(PROSE: What's Past is Prologue, The Note) As they approached their respective regenerations, the First Doctor and the Twelfth Doctor met Archibald Hamish Lethbridge-Stewart, a relative of Alistair who was slated to die alongside a German soldier in Ypres on Christmas.The two Doctors promised that they would check up on his family, but the Twelfth Doctor adjusted Archibald's time period slightly so that time resumed for Archibald and his opponent a couple of hours after Archibald left.
Henry Barns, who had gone home early, was unaware this hadn't happened and went to the moors to warn the other cadets about a stranger spotted around there; he was then held prisoner by the man, escaped murderer Jim Cliskey.Lethbridge-Stewart had a few extraterrestrial encounters in his early life, but they were all forgotten.A turning point in his life was the Great Intelligence's invasion of London, where he met the Second Doctor and Anne Travers and was inspired to defend Earth from alien threats.After the Third Doctor's regeneration — which the Brigadier witnessed — the Doctor became more distanced from Alistair and UNIT.After several adventures with later incarnations of the Doctor, the Brigadier retired from UNIT and became a teacher at Brendon Public School.