This week, we're gearing up for 9, Shane Acker's film about nine animated rag dolls, each known only by their number. With that in mind, we list 16 other characters who have numerical monikers.
Leaving aside characters with alphanumeric names (like Star Wars' R2-D2 and C-3PO), characters who also have serials number imparted to them by their governments but are not generally addressed as such (as in Nineteen Eighty-Four and The Giver), and characters whose first names happen to mean a number in a different language (as with many of the characters in Stardust and Mobile Suit Gundam), there are several characters who are either designated with or often called by a number:
Number One (Star Trek "The Cage"/"The Menagerie"): More than two decades before Captain Picard started referring to William Riker as "Number One," Majel Barrett filmed the original Star Trek pilot, where her character was known only as Number One. Like Riker, Number One was the Enterprise's first officer, but the novel Vulcan's Glory suggests Number One was her actual name, given to her because she possessed the top intellect of her planet's generation.
Number 5 (Short Circuit): Although roboticists Newton Crosby and Ben Jabituya were out to create artificial intelligence, they probably didn't expect any of their prototypes to suddenly gain sentience, and so assigned them numbers in lieu of names. But after prototype Number 5 becomes self-aware (and escapes the clutched of the US military), he decides that, as a living being, he should have a name, and calls himself Johnny Five.
Fifth (Stargate SG-1): One of the few characters with an ordinal number for a name, Fifth gets his name in a fairly straightforward manner: he's the fifth human-form Replicator to be created on the planet Halla.
V (V for Vendetta): Most people who live through encounters with the mysterious anarchist V think they're addressing him by a letter, and his propensity for using V-based alliterations when introducing himself seems to confirm this. But it's much more likely that V derives his name from the source of his vendetta; when he was subjected to medical experimentation at the Larkhill Resettlement Camp, he was the man in room five — marked with the Roman numeral "V."
Number Six (The Prisoner): Residents of the mysterious Village are known by a number rather than their actual names — including at least 16 individuals known only as "Number Two" — probably to protect the secrets they all inevitably carry. Number Six, the titular prisoner, protests in the opening that he's a free man, not a number, but it's implied that Number Six may be known by yet another number: Number One.
The Cylons (Battlestar Galactica): The creators of Battlestar Galactica have said that cylon Number Six is a tribute to The Prisoner, and it follows that each humanoid cylon model would have its own number, with the notable exception of the Final Five. Most cylon models are known collectively by a human name as well (the Sharons, the Leobens, the D'Annas), but individual Sixes tend to have individual human names, like Natalie, Caprica, Shelly, and Gina, perhaps because of they are so often used as infiltration agents.
Seven of Nine (Voyager): Names designate individuality, a concept the Borg have no use for, but sometimes it is convenient for the Collective to identify individual Borg drones. So when the formerly human Annika Hansen was assimilated into the Collective, she was given the designation Seven of Nine, Tertiary Adjunct of Unimatrix Zero-One. Even once she was unhooked from the hive mind, she preferred the shortened "Seven of Nine" to her human name, the latter of which she does not take up again until her Borg implants are completely destroyed.
Eight (The Specials): It's fairly obvious how Eight earned its superhero name. A hive mind, Eight consists of eight individual bodies who can physically act independent of one another, but share a single consciousness.
Thirteen (House): As long as we're labeling House as science fiction, we may as well mention Dr. Remy Hadley, better known as Thirteen. In one of his trademark moves to dehumanize his fellowship applicants, Dr. House assigned each applicant a number (and occasionally a humiliating nickname). Thirteen really took to the numerical naming system, refusing to divulge her actual name to her fellow applicants, and continuing to answer to Thirteen long after she'd earned a place on House's team.