John Bingham

John Michael Ward Bingham, 7th Baron Clanmorris of Newbrook, was an engineer, former MI5 spy, and an English novelist who published thrillers, detective novels, spy novels, and screen plays. - Wikipedia

Following a spell as a journalist, Bingham was recruited into MI5 by
Maxwell Knight. One of his younger colleagues was David Cornwell, who was
inspired by Bingham’s success as an author of fiction to become a novelist
himself, under the name John le Carré. Le Carré subsequently
acknowledged that Bingham was a key inspiration for his most famous
character, the spy George Smiley. [From the Introduction by Martin Edwards to The Christmas Card Crime and Other Stories, 2018]