Born the son of an antiquarian bookseller in London, he was first introduced to cryptography when his father showed him a copy of Edgar Allan Poe's story, "The Gold-Bug". From this early interest, he demonstrated his skill at codebreaking at an early age by deciphering his father's secret price codes.
His father, Benjamin Marks, was joint owner of the Marks & Co bookshop at 84 Charing Cross Road, which achieved international fame with the 1970 book of that title by New York writer Helene Hanff and the later plays and movie.
As a teenager, he earned pocket money by setting the notoriously difficult Times cryptic crossword. ..