This page contains information regarding Star Trek: Strange New Worlds, and thus may contain spoilers.
Lieutenant Commander Una Chin-Riley, commonly known professionally as Number One, was a female Illyrian Starfleet command division officer who lived during the mid-23rd century. Through the 2250s, she served aboard the USS Enterprise as Christopher Pike's first officer and helmsman. (TOS: "The Cage"; DIS: "An Obol for Charon")
Chin-Riley was born on an Illyrian colony in the early 23rd century. As a member of the Illyrian species, Chin-Riley was genetically enhanced. Early on in life, she dreamed of joining Starfleet; however, due to the Federation ban on genetic engineering, she had to hide her true nature and history. (SNW: "Ghosts of Illyria")
By the mid-23rd century, Chin-Riley joined Starfleet and, as an ensign, was assigned to the USS Martin Luther King Jr. During her assignment aboard the "King Junior", she was involved in the rescue of La'an Noonien-Singh. (SNW: "Strange New Worlds")
By 2254, she served under the command of Captain Christopher Pike. As well as being the ship's helmsman, Una served as its first officer, and went professionally by the name "Number One". (ST: "Q&A", TOS: "The Cage")
In 2254, Number One 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")
At the time, she was considered one of the most experienced members of the crew. According to the Talosian magistrate known as The Keeper, she had "the superior mind and would produce highly intelligent children", adding that, "although she seems to lack emotion, this is largely a pretense. She has often had fantasies involving [Pike]." (TOS: "The Cage")
With Pike kidnapped by the Talosians, Number One 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. Number One 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 thirteen 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 Number One 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")
In 2258, 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, Number One, 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, Number One and the others who knew of the Discovery's fate were sworn to never speak of the Discovery or its crew again.
In 2259, the Enterprise returned to Earth for scheduled maintenance.
Because she did not deal well with downtime, Number One was assigned to command the USS Archer and initiate a first contact mission to Kiley 279 after Starfleet detected signs of warp drive on the planet. However, the Kiley had in fact developed a warp bomb based on observations made from the battle near Xahea. The Kiley reacted negatively towards the first contact overtures and Number One, as well as two other members of the Archer's crew were held captive by the Kiley.
Chin-Riley 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")
She also enjoyed spicy food. When she met Pike on Discovery, she ordered a cheeseburger and french fries with habanero sauce. (DIS: "An Obol for Charon") Her comfort food, however, was strawberries. (SNW: "Ghosts of Illyria")
As a member of the Illyrian species, Chin-Riley was genetically enhanced as a child. Her physical strength was greatly improved, allowing her to carry a grown person with no visible effort, while her immune system could literally burn out infectious agent from her body without having to rely on antibodies. (SNW: "Ghosts of Illyria")
- Prior to 2254:
- 2256–2257: Along with the rest of the Enterprise crew, sits out the Federation-Klingon War
- 2257: Travels to the USS Discovery to update Captain Pike on the status of Spock and the Enterprise
- 2258: Takes part in the Battle near Xahea
- Assigned to the USS Archer
- Reassigned back to the Enterprise as first officer
Number One was originally portrayed by Majel Barrett in the Star Trek 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 facade." 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".
According to The Autobiography of Mr. Spock, Una's full name is Una Chin-Riley, a fact later revealed in the Strange New Worlds premiere episode "Strange New Worlds".
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. The novel The Enterprise War describes her as having been raised in Illyrian colonies and thus, while not actually being Illyrian herself, having adapted much of that species' emotional self-control. Her actually being Illyrian and raised in an Illyrian colony was confirmed canon in SNW: "Ghosts of Illyria".
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.
In the first issue of the 2013 comic series Star Trek: New Visions, Kirk, Spock, and McCoy report to a commodore who is not named but is clearly Number One and Spock did say it was pleasant to see her again.
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.