Rover was only named onscreen in one episode, "The Schizoid Man", but the name appears throughout the scripts. In the novel The Prisoner: Number Two by David McDaniel, based upon the series, the name Guardian was used instead of Rover.
Rover was depicted as a large white inflatable balloon, not quite fully inflated, with a flexible skin. Rover would often produce a muffled roar sound when attacking. It would also sometimes emit a strange light display / luminescence from its interior. Once released, Rover could bounce and glide across the land and sea for a long range and at high speed, faster than a vehicle or boat.
Rover behaves as if it were a self-aware or quasi-intelligent entity and can interact with its surroundings, adjusting to and anticipating the actions of, Number 6 and other characters. No apparent direct control was ever shown to be exerted over it by the controllers of the Village, other than to release it. Rover would occasionally be seen outside of its normal environment, sitting placidly in rooms, in Number 2's chair, roaming the streets of The Village, or being studied by unidentified persons in "secret" areas of The Village.
Rover possessed considerable strength, and was able, if necessary, to incapacitate people either by blunt force impacts, or through suffocation by pinning the subject down.
In the first episode the rest of the villagers appear to freeze in time while Rover attacks an unidentified man (played by Seamus Byrne). This happens again at the start of "Checkmate," the ninth episode.
The use of Rover appeared to be both intimidatory and functional. Following encounters in the early episodes, where Rover physically interacts with prisoners, the Number 6 character gradually gives up trying to defeat Rover directly, and its mere presence is often enough to achieve its objectives.
While Rover primarily prevented escapes, it also served as a guard agent or herder when a character was required to take a certain action or direction, or to prevent their access to some part of the Village. In the cases where Rover incapacitated a prisoner, it also appeared that it had the capability of transporting their limp body. Occasionally, if attacking somebody in the water, the incapacitated victim (including Number 6 on one occasion in "Free for All"), would be carried back to the shore by what appeared to be three smaller Rovers.
Rover could be summoned at the direction of the control room, with a stock scene of its inflation shown before its appearance, although this sequence could also be omitted with Rover appearing spontaneously. It would be inflated beneath the sea, although its first appearance came as being inflated from the Village fountain. No explanation was ever made as to where Rover went after its mission had been completed, aside from a single scene in "Free For All" where Rover appears to return to the bottom of the sea (simply a reverse reel of the spawning sequence).
Several aspects of how Rover worked were never revealed in the series beyond the primary actions in subduing prisoners, in which task it was apparently extremely effective.
Open questions surrounding Rover suggest that its use in the series was a variation of the deus ex machina type of plot device, used as a means to give a reason as to why the Village is so successful in coercing the inhabitants and preventing escape, without having to waste unnecessary screen time explaining this method. The other methods of control of the Village, such as surveillance, mind-control and double agents, are explored in much more detail in the TV series than Rover.
Rover was originally supposed to have been a robotic, wheeled device with a siren. It resembled a circular inflatable swimming pool topped with a black-and-white segmented dome. Although a prop was constructed, it did not work properly, and sank in the waters off Portmeirion during the initial stages of filming.
The final version of Rover was inspired by a weather balloon seen above Portmeirion by Patrick McGoohan. The balloon was dragged across the set with wires, with the wires and the attachment point sometimes being visible. Several approach scenes were filmed through the use of reversing a film of the balloon being towed away from the camera, although the balloon was often also filmed from the side being towed in direction of travel.
Rover is last seen in "Fall Out". While the rocket is being launched, Rover drops down a hole to an underground 'cave' like area, where it shrinks to a small size and becomes still as if it is deactivating itself now that it is no longer needed in The Village. However, this scene was not in the script and was inserted to give Rover its finale.
Rover has become an icon of the series, and has been referenced numerous times in popular culture, such as in the Simpsons episodes "The Joy of Sect" (where it envelops Hans Moleman) and "The Computer Wore Menace Shoes" (in which Homer simply pops it with a plastic spork, thus prompting Number 2 to question its effectiveness). The DVD box set of the series includes an advert for Renault cars (not Rover cars, as has been widely reported), in which a man in Prisoner style clothing escapes from The Village by outmaneuvering a version of Rover depicted not as a balloon, but a large solid white ball.
The writers of the television series Lost have made mention on numerous occasions that the Rover was the inspiration for the "Smoke Monster."
Rover appeared in the 1984 CP/M edition of Crowther, Woods' Colossal Cave text adventure game, either in the Vault (player gives wrong magic word) or the Computer Center (player takes posters from the wall).
In Mystery Science Theater 3000's presentation of Laserblast, Tom Servo identifies an inflated white pool toy as "Rover from The Prisoner!"
In Xavier Mauméjean's short story, "Be Seeing You!", from the second volume of the Tales of the Shadowmen anthology series, the original Rover from 1912 is made of metal and propelled by steam, and is stated as being designed by the character of Cavor from H. G. Wells' novel The First Men in the Moon.
Rover appears in Liverpool quartet Clinic's video for their single 'Harvest.'
Remake: "The Beast"
Rover appears in the 2009 mini-series remake of The Prisoner. This version of Rover is only ever referred to by Two as "The Beast". It is much larger than the original, described as being more of a presence than a material thing. In the final episode, The Beast is revealed to be an embodiment of 6's hidden desire to stay in the Village, thus stopping any attempt at escape made by himself or others.