The term was first used in “Rough Justice,” a story credited to both Alan Moore and Alan Davis published in July 1983 by Marvel UK in the anthology comic The Daredevils (and was later reprinted in the Captain Britain trade paperback). Saturnyne uses the term to differentiate Brian Braddock, the Captain Britain of the regular Marvel Comics universe, from the other members of the Captain Britain Corps, each of which inhabit different universes. The designation was later used by the American branch of Marvel Comics in the Excalibur title, which frequently referenced Captain Britain’s early UK-published adventures. This comic was written by Chris Claremont, who had created Captain Britain, and by Alan Davis, the artist on the UK-published series.
Alan Moore is usually credited with creating the term (for example by Marvel editor Tom Brevoort). However, Alan Davis has stated that the designation of Earth 616 was actually first made by Dave Thorpe, the previous writer of the UK-published Captain Britain stories.
In addition, a difference of opinion exists regarding the selection of the number 616. In 2005, Alan Moore’s son-in-law John Reppion (who is married to Alan Moore’s daughter Leah Moore), stated on an Internet message board that the number 616 was arbitrarily chosen by Moore and had no significant meaning, saying it “was just a random number of no significance chosen because people always seemed to be talking about ‘earth 2’ or ‘earth 4’ but never any higher numbers.” However, Alan Davis has said that it comes from 616, a variation on the Number of the Beast, picked because Dave Thorpe “wasn’t a fan of the modern superhero genre” and expressed this in his stories, “such as recording his opinion of the Marvel Universe with the designation 616.”