2. Brigadier Sir Alistair Gordon Lethbridge-Stewart
Brigadier Sir Alistair Gordon Lethbridge-Stewart, or just 'the Brigadier' for short, was possibly the Doctor's closest companion throughout the Classic Series. The Brigadier first met the Doctor all the way back in his scone incarnation, played by Patrick Troughton, and he easily accepted the story about who the Doctor was and what he stood for. When the Third Doctor was exiled to Earth for the majority of his reign, he joined forces with the Brigadier, who was assigned to a military intelligence group called UNIT, to aid him against Earth's latest extraterrestrial excursions.The Doctor even became an adviser to UNIT and his partnership with the Brigadier subsequently extended into his future incarnations. In the revived series, the Brigadier has been fondly remembered by the Doctor and he lives on through his daughter, Kate Stewart, who stands as the head of UNIT in the present day. The Brigadier himself was given the farewell he deserves when, as a Cyberman in the Series 8 finale Death in Heaven, the Twelfth Doctor finally rendered him the salute he had always been aiming for.