Originally played by iconic Star Trek actress Majel Barrett, the character known as Number One is now played by Rebecca Romijn in Star Trek: Strange New Worlds. Una Chin-Riley, better known professionally as Number One, serves as the first officer on the USS Enterprise under the command of Captain Christopher Pike (Anson Mount). Number One first appeared in Star Trek's original unaired pilot, called "The Cage." While this episode was not made available to the public until 1986, footage from "The Cage" was incorporated into the TOS two-part episode, "The Menagerie."

Rebecca Romijn first began playing Number One in Star Trek: Discovery season 2, alongside Anson Mount's Captain Pike and Ethan Peck's Spock. As seen in TOS, Number One was an enigmatic character with no backstory to speak of. Strange New Worlds has given Una a compelling backstory that connects to Star Trek lore. Una is a member of the Illyrian species, meaning that she has been genetically enhanced with superior strength and resistance to disease. Because genetic engineering was banned in the Federation, Una had to lie on her Starfleet application.

Rebecca Romijn's Number One In Star Trek: Strange New Worlds Explained

Despite lying to get into Starfleet Academy, Number One has an exemplary Starfleet record. Una and Captain Pike are close friends, and she is one of the few people who knows about his tragic future. Number One has received several medals and awards from Starfleet and is one of the most experienced officers aboard the Enterprise. Though she was eventually court-martialed for lying on her Starfleet application, she ultimately won her trial and was reinstated to her position. As revealed in "Those Old Scientists," Number One appears on future Starfleet recruitment posters with the phrase "Ad Astra per Aspera."

Actress and former model Rebecca Romijn is best known for starring as the shapeshifting mutant Mystique in X-Men, X2: X-Men United, and X-Men: The Last Stand. She also starred as Laurie/Lily in the 2002 movie Femme Fatale, and played Joan in The Punisher in 2004. She has appeared in several other movies and television shows, including a lengthy run on Ugly Betty and a starring role as Eve Baird on TNT's The Librarians. In 2007, she married Jerry O'Connell, who voices Commander Jack Ransom on Star Trek: Lower Decks. Romijn has provided the voice for Lois Lane in several DC Universe animated movies, alongside O'Connell's Superman.

How Rebecca Romijn Changed Number One From Star Trek: TOS For The Better

Much like Jeffrey Hunter's version of Captain Pike, Number One did not get much screen time in Star Trek: The Original Series, so the character was essentially a blank slate. Majel Barrett's Number One did not even have a name and never appeared again after "The Cage" and "The Menagerie." Strange New Worlds has filled in much of the character's backstory, making her more compelling and three-dimensional. While Barrett's Number One had the potential to be a great character, that potential was never realized after that initial pilot was scrapped.

Rebecca Romijn's Una Chin-Riley has proven to be a competent and likable character who has more than earned her place as First Officer on the Enterprise. She's perfectly capable of commanding the ship when Pike has duties elsewhere, and always keeps calm in a crisis. Una takes her duties as First Officer very seriously, which is one of the reasons she and Security Cheif La'an Noonien-Singh (Christina Chong) get along so well. The pair's friendship helps humanize Una as a character. Star Trek: Strange New Worlds and Rebecca Romijn have reinvented Number One for the better, and she has quickly become one of Star Trek's best first officers.

Star Trek: Strange New Worlds season 2 streams Thursdays on Paramount+.