| Number One | |
 Number One in 2264 | |
| Full name: | Number One |
| Species: | Terran |
| Gender: | Female |
| Homeworld: | Earth |
| Birthplace: | Earth |
| Died: | 2264 |
| Affiliation: | Terran Empire, Imperial Starfleet |
| Career | |
| Occupation: | Imperial Starfleet officer |
| Final Assignment: | First officer, ISS Enterprise |
| Rank: | Commander |
- For the primary universe counterpart, see Una.
In the mirror universe, Number One was a Terran female who served in the Imperial Starfleet of the Terran Empire during the mid 23rd century. She was the first officer of the ISS Enterprise under the command of Captain Christopher Pike.
During her service aboard the Enterprise, the Talosians captured Pike. They had used a distress call to lure the Enterprise to the planet with the intention of having Pike mate with Vina so as to create a race of Terran slaves. However, Pike rejected Vina, refusing to mate with an "insipid human female." In response, both Number One and J. Mia Colt were offered to Pike as potential mates.
By 2264, Number One had numerous conflicts with Spock and had him reprimanded, leading Spock to request that Lieutenant Commander James T. Kirk eliminate her and promote him to the position of first officer of the Enterprise once he took command. Kirk agreed to these terms, killing Number One with the Tantalus field. (TOS - Mirror Universe short story: "The Greater Good")