Vernon Kell

…1909 under the leadership of Vernon Kell, then a captain in the British army, to identify and counteract German spies then working in Britain, which it did with great effect. Kell retired as a major general in 1924 and was later knighted but remained in charge of the agency until…

…derived from the name of Sir Vernon Kell, its chief from 1909 to 1940. MI5 makes no direct arrests but instead works secretly with the more publicized “Special Branch” of Scotland Yard.