O'Brien (The Web of Fear)

Private O'Brien was a soldier in the British Army. He took part in the fight against the Great Intelligence and its Robot Yeti in the London Underground. While trying to collect ammo from an army supply truck, O'Brien was killed when one of the Yeti shot him with its web gun. (TV: The Web of Fear)

Behind the scenes
O'Brien is only named in the dialogue for episode two; he is credited as "Soldier" in the end credits.