No Time To Die, with Daniel Craig set to bow out after his fifth outing in the role before a new actor takes up the prestigious 007 mantle.

Craig first debuted as Bond in Dr. No hit theaters, Fleming had published ten Bond stories, the first being Casino Royale. By 1962, the books had established a fairly firm backstory for their suave protagonist, including the explanation of the "00" status as designating an agent of the Secret Service who had been granted a license to kill in the line of duty.

Related: James Bond: Every Time 007 Quit The Secret Service (And Why)

In the movies, 2006's Casino Royale was the first time audiences were given an the books when it comes to Bond's 007 backstory, but switches things up for a more dramatic opening sequence. Bond still needs his double kills to become a "double-O," but these aren't the same "two villains" from the book.

Casino-Royale-End Cropped

Things get a little more complex when it comes to the meaning of the double-O designation itself. It seems Fleming was still working out the details by his third book in the series, Moonraker. Not until this novel was it confirmed that "00" agents carried the famous license to kill. Prior to these revelations, Fleming had simply established that two successful kills in the course of a job led to the "00" promotion - and even that remains somewhat unclear. Though Bond says in Casino Royale that he killed two people before he was given his elite status, he also says, "A Double O number in our Service means you've had to kill a chap in cold blood in the course of some assignment," suggesting it only takes one kill to earn the title.

In the films, Bond has been taking out enemies since Dr. No, operating under his "00" status from the beginning (until Lashana Lynch's Nomi, who is rumored to have filled the 007 role since Bond's retirement. If the reports are accurate, and Nomi is the new 007 rather than another "00" agent, the James Bond movies will have also established that the last number in the designation does not refer to the person themselves, but is a generic code that can be applied and reapplied to whatever agent fills the role.

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