April Dancer was originally to have been named Cookie Fortune. The name April Dancer is attributed to James Bond creator Ian Fleming, who had suggested the name for an UNCLE operative when he helped in the creation of "The Man from U.N.C.L.E. (1964)" prior to his death.
Leo G. Carroll, by appearing as Waverly in both UNCLE shows, became one of the first actors in the history of TV to play the same continuing character in more than one series.
The pilot for this series aired as a The Man from U.N.C.L.E. (1964) episode "The Moonglow Affair" in early 1966, with Mary Ann Mobley as April Dancer and Norman Fell as a much older and decidedly non-British Mark Slate.
Sam Rolfe wanted to leave the meaning of UNCLE ambiguous so it could be understood as a reference to "Uncle Sam" but, under pressure from the U.N.O., the producers added an end card reading, «We wish to thank the United Network Command for Law and Enforcement without whose assistance this program would not be possible.» U.N.C.L.E.'s archenemy was a vast organization known as THRUSH (originally named WASP in the series pilot movie). The series never explained the acronym THRUSH, but 'David McDaniel' in his MGM authorized novel "The Dagger Affair", revealed it was the Technological Hierarchy for the Removal of Undesirables and the Subjugation of Humanity,
April Dancer's "U.N.C.L.E. number" is 22, double that of Napoleon Solo's number which is 11.