Una, also known professionally as Number One, was a female Human Starfleet officer in the 23rd century. Since at least 2254, she served aboard the USS Enterprise as Christopher Pike's first officer. (TOS: "The Cage"; DIS: "An Obol for Charon").
At some point during her life, Una enlisted in Starfleet and was assigned to the command division aboard the USS Enterprise. Upon her assignment to the Enterprise, she witnessed a triple-mode high-amplitude Delta Scuti star on her first deep-space cruise that took her within a half light year of 99 Pegasi. (ST: "Q&A")
First officer of the USS Enterprise
By 2254, Una was promoted to the rank of lieutenant commander and was serving under the command of Captain Christopher Pike. As well as being one of the ship's helmsmen, Una was its first officer. (ST: "Q&A", TOS: "The Cage")
In 2254, Una greeted Ensign Spock, who joined the crew of the Enterprise after departing from Starbase 40. She encouraged him to barrage her with questions, which he returned in kind. While talking, however, the two were trapped in a turbolift, where they bonded and Una gave advice to the young officer before they were rescued by Lieutenant Amin. (ST: "Q&A")
She was one of the most experienced members of the crew. According to the Talosian magistrate known as The Keeper, she had exceptional intelligence and rationality, while her seeming lack of emotion was largely a pretense concealing fantasies that involved Captain Pike. (TOS: "The Cage")
With Pike kidnapped by the Talosians, Una led the effort to rescue him, first by unsuccessfully attempting to use a laser cannon to blast open an entry to a Talosian underground lair where Pike was being held, and then by using the transporter in an attempt to infiltrate this lair. Una was subsequently kidnapped, along with Yeoman Colt, for the purpose of providing Pike with a mate with whom he could procreate. In response to this, Una set her laser pistol to overload, telling the Talosian Keeper that it was wrong to keep a colony of Humans as slaves, and that they would rather die. This, combined with an examination of the Enterprise's historical records, convinced the Talosians that Humans' unique hatred of captivity made them nonviable subjects, and they were subsequently allowed to return to the Enterprise. (TOS: "The Cage")
Footage of her experience aboard the Enterprise under Captain Pike during the original visit to Talos IV, from 13 years prior, was transmitted from that planet during Spock's fictional court martial aboard the same ship in 2267. (TOS: "The Menagerie, Part I", "The Menagerie, Part II")
In 2257, she remained with the ship while it underwent major repairs that year, but briefly visited Pike aboard the USS Discovery to provide him with information on Spock's recent escape from Starbase 5. The two officers sat and talked briefly as Una sat down to a meal in the mess hall. During their conversation, Una admitted that she went through unofficial channels to obtain the information, noting that the entire situation was extremely odd. Una stated plainly that she was not going to let Spock go without a fight and Pike noted that as usual they both were in agreement. Before they parted she warned Pike to be careful and Pike told her the same. She returned to the Enterprise shortly thereafter. (DIS: "An Obol for Charon")
Battle with Control
Following the mission to get a time crystal from the monastery on Boreth, Christopher Pike asked R.A. Bryce to send a message to the Enterprise's XO, Una, to have the Enterprise rendezvous with the Discovery to take on the Discovery's crew. (DIS: "Through the Valley of Shadows")
After the disappearance of the Discovery, Pike, Ash Tyler, and Number One were debriefed at Starfleet Command in San Francisco. Following the debriefing, Una and the others who knew of the Discovery's fate were sworn to never speak of the Discovery or its crew again.
Una secretly enjoyed the music of Gilbert and Sullivan. When trapped in a turbolift with Spock on his first day on the Enterprise, she sang "I Am the Very Model of a Modern Major-General", but ordered Spock to forget it. (ST: "Q&A")
- Prior to 2254: Assigned to the USS Enterprise under Captain Christopher Pike as first officer
- 2256–2257: Along with the rest of the Enterprise crew, sits out the Federation-Klingon War
"What are the three most salient facts about Captain Pike?"
"One, his capacity for hearing out another point of view is exceeded only by his willingness to change his own once he's heard you out. Two, even though he is the most heavily decorated fighting captain in Starfleet, he views resorting to force as an admission of failure. And three... he is utterly unsentimental except when it comes to horses."
"It's wrong to create a race of Humans to keep as slaves."
"Who would have been Eve?"
"Welcome aboard Discovery, Number One."
"Cheeseburger. Fries. Habanero sauce."
"You want to order some lighter fluid with that?"
"That goes with the shake."
"Welcome home, Captain."
"Good to be back. Wish it were under better circumstances."
"Don't we all."
"All major systems are back online, and we'll have no more holographic communications...ever."
"Probably for the best."
- - Una, Christopher Pike, and Katrina Cornwell, on Pike's return to the Enterprise (DIS: "Such Sweet Sorrow")
"Actually, our odds might be a little better than that. I took the liberty of retrofitting our shuttle and landing pod complement with enhanced phasers, and I commandeered the new experimental tactical flyers, assuming the shit would hit the fan."
"Well done, Number One."
"In English please. I can't blow a path through what you're saying."
"Captain, plans A and B didn't work. We're now into the 'Hail Mary' part of the operation."
"That's been just about everything today."
"Where to, Number One?"
"You're the captain, Captain."
"I hear we discovered a new moon at Edrin II."
"That we did, sir."
"Thank You, Number One. In that case, let's give her a spin. That sound good to you, Mr. Spock?"
"Yes, Captain. Let us see what the future holds."
"Ready for warp, sir."
- - Christopher Pike, Una, and Spock, on the Enterprise's next destination (DIS: "Such Sweet Sorrow, Part 2")
|First officers of the starships Enterprise|
|Enterprise NX-01:||Tucker • T'Pol • Sato|
|USS Enterprise:||Pike • Una • Spock • Decker • Saavik (as a trainee) • Thelin|
|USS Enterprise-D:||Riker • Kurn • Shelby • Data • Worf|
|ISS Enterprise NX-01:||Archer|
|ISS Enterprise NCC-1701:||Spock|
|USS Enterprise:||Spock • Kirk|
Una was originally portrayed by Majel Barrett in the Star Trek: The Original Series pilot, "The Cage", but credited as M. Leigh Hudec for her subsequent archival appearance featured in both episodes of "The Menagerie". When her character was reintroduced for Star Trek: Discovery, and its subsequent spin-offs, she was portrayed by Rebecca Romijn.
In the original version of the series outline Star Trek is... (as reprinted in The Making of Star Trek, pp. 22-30), Number One was initially described as "a glacierlike, efficient female who serves as ship's Executive Officer." (The Making of Star Trek, p. 24) A more detailed description of the character from exactly the same document stated;
- The Executive Officer
- Never referred to as anything but "Number One", this officer is female. Almost mysteriously female, in fact – slim and dark in a Nile Valley way, age uncertain, one of those women who will always look the same between years twenty and fifty. An extraordinarily efficient officer, "Number One" enjoys playing it expressionless, cool – is probably Robert April's superior in detailed knowledge of the equipment, departments, and personnel aboard the vessel. When Captain April leaves the craft, "Number One" moves up to Acting Captain. (The Making of Star Trek, p. 29)
In the scripts of "The Cage", Number One was described as "Female, slim and dark in a Nile Valley way, age uncertain, one of those women who will always look the same between the ages of twenty and fifty [....] Almost glacier-like in her imperturbability and precision. From time to time we'll wonder just how much female exists under that icy façade." She was also scripted to be slightly more wary of J.M. Colt than she is in the final version of the episode, such as being initially reluctant about allowing her to join a landing party assigned to rescue the captain. 
Number One was dropped from the series as NBC executives did not respond well to her character. Reactions to her in the screen test of "The Cage" were also poor (by the women more negatively than the men, according to Gene Roddenberry). Her highly logical, steel-trap mind was given to the character of Spock in "Where No Man Has Gone Before" and maintained there onward.
Although Majel Barrett-Roddenberry was credited as Majel Barrett in the unaired episode "The Cage", she was credited as "M. Leigh Hudec" – Barrett's birth name – in the televised two-part episode "The Menagerie, Part I" and "The Menagerie, Part II", because the production team was endeavoring to hide from NBC the fact that the actress, not to be signed for either the second pilot or the regular show as had been demanded by the network, had actually returned to Star Trek: The Original Series as the recurring Nurse Christine Chapel by Gene Roddenberry's doing. (Inside Star Trek: The Real Story, 1997, pp. 223-224; These Are the Voyages: TOS Season One, 1st ed, pp. 25-27) An unintended ironic twist in Star Trek history was that when Roddenberry surreptitiously brought the natural brunette Barrett back on the Original Series, he had her also disguised as a blonde to mislead the NBC network executives, who adamantly did not want her back on the show, whereas the natural blonde Romijn had to have her hair dyed to have her appear as the brunette Number One in Discovery.
Regarding Number One's rank in the pilot, and in later Star Trek incarnations, it was rare for a lieutenant to serve as the first officer of a starship. The likely reason for this was that, when Gene Roddenberry first created Star Trek, the first rank structure he employed was based on the system used in the 18th and 19th century British navy, in which a ship's second in command was generally a first lieutenant in the sense of the most senior lieutenant, rather than 20th century naval ranks we have come to associate with Starfleet. In the character's subsequent appearances in Star Trek: Discovery and Star Trek: Short Treks, she holds the rank of lieutenant commander.
In an interview with TrekCore, the co-writer of "Such Sweet Sorrow, Part 2" and Star Trek: Discovery third season co-showrunner Michelle Paradise confirmed that Christopher Pike called Number One "Una" in that episode.  This is one of several names which had been used for this character in non-canon material. Subtitles on Netflix and the second season Blu-ray release misspelled it as "Noona" (the Netflix subtitles have since been corrected), while the CBSAA captions say that he merely said "and, uh..." while transitioning to a question directed at Admiral Cornwell. Dialogue and PADD graphics in the Star Trek: Short Treks episode "Q&A" definitively confirm that Number One's name is "Una," and that she insists on being addressed as "Number One".
In the Marvel Star Trek: Early Voyages comic book series, this character was named Lieutenant Commander Robbins. Her first name was interrupted by other dialogue, but starts with "Eure-."
The novel Vulcan's Glory, by Star Trek: The Original Series writer D.C. Fontana, suggested this character's moniker was not simply a nickname or title – she was an Illyrian who was called "Number One," as the best intellect among her generation. The novels The Children of Kings and Child of Two Worlds explain that Number One does have a given name, but it's difficult to pronounce for non-Illyrians; the former suggests that she liked to be called by this name rather than her own as it enabled her to maintain a professional relationship with her captain.
In the novel Captain to Captain she is referred to as "Una". The novel explained that she had adopted the name Una as far back as her Academy days, due to her real name being all but impossible to pronounce. The name "Una" was also used in the Star Trek: Discovery novel Desperate Hours and was subsequently used in DIS: "Such Sweet Sorrow, Part 2" and ST: "Q&A".
Star Trek II: Biographies gives her real name as Leigh Hudec (after "M. Leigh Hudec", the name under which Majel Barrett was credited in The Cage).
Peter David's New Frontier series of novels had a character named "Morgan Primus" who was an immortal like Flint (from TOS: "Requiem for Methuselah") and was the mother of Robin Lefler. It is hinted that she and Number One are the same person.
In the IDW Publishing comic Star Trek: Romulans - Schism, she is a commodore in command of the USS Yorktown testing the cloaking device stolen from the Romulans during the events of "The Enterprise Incident". No name is mentioned.
The novel The Enterprise War describes her as having been raised in the Illyrian colonies and thus, while not actually being Illyrian herself, having adapted much of that species' emotional self-control.
In Who's Who in Star Trek, Number One is said to have been descended from colonists on a planet inhabited by telepathic humanoids who are peaceful. She is described as having entered Starfleet after saving the life of Earth's leader when his shuttle crashed on her planet, he having waived all psychological and physical testing on her behalf. She is also described as having suffered severe injuries just prior to the end of Pike's tenure as captain of the Enterprise, forcing her to retire from exploration and become an instructor at Starfleet Academy.
According to The Autobiography of Mr. Spock, Una's full name is Una Chin-Riley.