In 2019, the second season of Star Trek: Discovery, set during Pike's tenure as captain of the Enterprise, featured Number One's first on-screen appearance in 53 years, now played by Rebecca Romijn.

Although not shown on-screen, it is implied that Number One briefly takes command of the Enterprise when Captain Pike and his landing party first beam down to Talos IV.

[5] During the development of the first pilot for Star Trek: The Original Series ("The Cage"), Roddenberry wrote the part of Number One specifically for Barrett.

"[14] In his book Inside Star Trek: The Real Story, Solow suggests the network had no problem with the character, but was infuriated when a relatively unknown actress was cast simply because she was having an affair with Roddenberry.

[15] Because of NBC's rare order of a second pilot, Roddenberry compromised by eliminating Number One,[16] but aspects of her character—specifically, her cool demeanor and logical nature—were merged into Spock (who does appear in "The Cage") during the regular run of the series.

[1] On the series Star Trek: The Next Generation, Commander William Riker is usually (and informally) called "Number One" by Captain Picard, because of his position as first officer on the USS Enterprise.

On the series Star Trek: Discovery, set in 2256 (two years after the events of "The Cage"), female Commander Michael Burnham is referred to as "Number One" by Captain Georgiou, because of her position as first officer on the USS Shenzhou.

[19] Number One was first referred to as "Una" in the non-canonical 2016 novel trilogy Star Trek: Legacies, which was published by Pocket Books to mark the original series's 50th anniversary.

[20] Barrett's role as Number One in the first pilot led to her being cast as Nurse Chapel in the original Star Trek television series.