David John Moore Cornwell , better known by his pen name John le Carré , was an English author, best known for his espionage novels, many of which were successfully adapted for film or television. " sophisticated, morally ambiguous writer", he is considered one of the greatest novelists of the postwar era. During the 1950s and 1960s, he worked for both the Security Service and the Secret Intelligence Service . Near the end of his life, due to his strong disapproval of Brexit, he took out Irish citizenship, which was possible due to his having an Irish grandparent.