Colonel - later Brigadier - Alistair Gordon Lethbridge Stewart was the commanding officer of UNIT, an international body tasked with investigating extra-terrestrial threats. He first met the Second Doctor - helping him free London from the clutches of the Great Intelligence and the Cybermen. When the Third Doctor was exiled to Earth, he became UNIT's unofficial scientific advisor, providing the Brigadier with much needed support against Autons, Sea Devils, Daleks and the Master. Later in life, he retired from UNIT and taught at a boarding school. Later still he aided the Seventh Doctor in vanquishing Morgaine, before settling down for good with his wife Doris. It was during his battle with the Silence, that the Eleventh Doctor learned the Brigadier had passed away peacefully in his sleep.