1. The Mysterons are the inhabitants of Mars and the enemy force in the kid's TV show Captain Scarlet.
We aren't given a very deep background into Mysteron culture in the show, but it is apparent from the first episode that they were a peaceful people until Captain Black's fateful error. The very highly-developed technology would suggest that they are a race of scientists and engineers.
For a peaceful people however they can be terribly devious and deceptive, as their political ventures during negotiations with The Moon and Earth itself have proved, as both times the negotiations turned sour after Mysteron scheming was uncovered.
Appearance
Far from being little green men, The Mysterons in their natural form are in fact completely invisible. Like many details about them, the reason for this is left open to speculation. Perhaps they have evolved into creatures of pure energy, maybe Gerry Anderson couldn't afford another set of costumes and puppets.
Imitation
A lot of newbie Captain Scarlet geeks have a misconception that The Mysterons take over the minds of people. This is completely untrue (except in the weird case of Captain Black) as 99.9% of the time that The Mysterons plant one of their agents on Earth, the agent is often seen to be standing over the corpse of the person s/he was copied from.
Mysterons can only make copies of people or objects that have been killed or destroyed. (Captain Black aside of course) After this destruction, a dual-beam of energy is shone over the remains from Mars, bringing about the re-generation. It is never said what exactly is contained in the beam but one could logically deduct that it contains the actual Mysteron who will be inhabiting the body.
The Mysterons seem to communicate as one, in a similar way to The Borg from Star Trek. However unlike The Borg it seems that the voice of The Mysterons is merely a spokesperson for their race (most likely Captain Black) rather than the voice of some sort of hive mind.
The Voice Of The Mysterons was spoken by one Donald Gray, who also played Colonel White and, unsurprisingly, Captain Black
Detection and Destruction
Detecting and Destroying a Mysteron infiltrator is a matter of exploiting The Mysteron's two most defining characteristics: They are impervious to X-rays and can only be destroyed by an intense electrical current.
The Mysteron detector is essentially a Polaroid camera that takes X-ray photographs. If the target is a human, a normal X-ray will develop. If it's a Mysteron, the photograph will develop as a normal black-and-white photograph would.
The Mysteron gun is a very short range weapon, as the user must be within a few feet of the victim to use it effectively. The gun is just a very highly-powered electrical discharge device, much like a stun gun or a cattle prod. Of course one must be careful when using it, as it would be just as effective upon humans as it would be on a Mysteron.
Source: http://www.imdb.com for the voice of The Mysterons.
Sites of interest:
http://www.captainscarlet.tv
http://www.fanderson.org.uk
2.
Captain Scarlet
Episode one
The first episode of Captain Scarlet, The Mysterons lays the foundations of what is to come over the following installments of this series.
We start in the Martian Exploration Vehicle on the surface of Mars. It is manned by the (still human) Captain Black and two young lieutenants (apparently the one in the red jumpsuit is called Lieutenant Dean. We don't find out the name of the one in the blue suit, but he looks to be the same puppet as was used for Gordon Tracy in Thunderbirds, but in any case they just seem to be stock puppets.) They're evidently seeking out life on Mars, but with not much luck. Still, they're determined to find the source of radio waves had detected coming from somewhere in the vicinity, and decide to try looking over one last ridge.
Upon going over the ridge, the three men find the Martian Complex they had been looking for. The beings inside (The Mysterons) spot the Martian Exploration Vehicle and after saying how the Earth men must be welcomed, decide to take a closer look.
Unfortunately for both the Earth and Martian beings, The Mysteron's investigation probes look suspiciously like gun mountings.
Lieutenant: They're obviously hostile!
Captain Black: Okay, Lieutenant, let them have it!
And with them two fateful lines, the Earth men leveled the Martian complex, only to watch in disbelief as a mystical beam reconstructs the complex to a state as though it had never been fired on in the first place.
The Mysterons (presumable over radio) say that they are a peaceful people and their firing upon the Martian complex was an act of war. One of the crew of the Martian Exploration Vehicle (Captain Black) would become their representative on Earth. (Cue Captain Black suddenly gaining a five o'clock shadow and extremely pale complexion.) As The Mysteron's first act of retaliation, they plan to assassinate the World President of Earth.
Now a new scene, we are on Spectrum's airborne headquarters, Cloudbase. Colonel White, the Commander In Chief, orders Lieutenant Green to launch all Angels.
After this, we cut to a Spectrum Saloon Vehicle, occupied by Captain Brown and Captain Scarlet. They are on their way to rendez-vu with the World President. After a brief discussion between the two captains over whether The Mysterons are really capable of the assassination, the saloon suddenly suffers a blow-out, sending it hurtling off the road and sending the two Captains to their deaths. But just as the camera falls on Captain Scarlet's body, we see it being dragged away, only for an identical copy of him to be seen standing next to it, quite unscathed.
Back on Cloudbase we see Colonel White telling Captain Scarlet what a lucky man he was to have survived the crash. Captain Scarlet tells the Colonel that the rendez-vu with the World President was a success, and that he is now being escorted through New York.
In New York, we see a motorcade, containing Captain Brown and the World President on their way to the Spectrum maximum security building. The streets are literally teeming with Spectrum personnel to ward off any assassination attempt. Upon entering the building, the two men go to their room where they will be in hiding for the next few weeks. After some chit-chat, Captain Brown all of a sudden goes very quiet and smoke starts pouring from under his collar. Suddenly he bursts in to flames. Cut to outside the building, which explodes, totally destroying it.
On Cloudbase again, we see the unharmed President and Colonel White explaining how the President managed to escape. It turns out the entire desk in the room was able to be retracted into a secure compartment in the wall. Colonel White remarks how very peculiar it was of Captain Brown to explode like that, and orders Captain Scarlet to take the President to London. Not long after Captain Scarlet takes off with the President, Lieutenant Green gets a report that the body of Captain Brown was found at the saloon crash site. In his wisdom, Colonel White decides something fishy is going on and orders Captain Scarlet to return to Cloudbase at once.
Captain Scarlet doesn't respond to the order to return, so Colonel white orders The Angels to make a dummy attack on Captain Scarlet's plane. This doesn't deter the Captain and when the President attempts to radio Cloudbase, Captain Scarlet knocks him out. Captain Scarlet ejects both men from the plane, and at gun point, gets in a car with the World President and drives off towards the London Car-Vu.
Back on the ground, Captain Blue drives into a gas station in a Spectrum Saloon Vehicle and requests a Spectrum Pursuit Vehicle (SPV). On board the SPV, Captain Blue sets off in pursuit of Captain Scarlet and the World President.
After arriving at the top of the 800-foot tall London Car-Vu, Captain Scarlet forces the World President to climb into a radio-antenna housing on the side of the Car-Vu. Still climbing the Car-Vu, Captain Blue radios Spectrum helicopter A42 and instructs the pilot to take out Captain Scarlet and rescue the world President. The camera cuts to the helicopter and shows that there is no pilot. The helicopter is under the control of the invisible Mysterons.
When Captain Blue arrives at the top of the Car-Vu, a brief shoot-out between him and Captain Scarlet, followed by the Mysteronised helicopter A42 shooting at Captain Blue. The Angels take out the Helicopter, which goes crashing into the Car-Vu. Captain Blue shoots Captain Scarlet, who falls 800 yards to earth. The world president is rescued and brought back to the ground just as the Car-Vu begins to collapse due to the crashed helicopter.
Back on Cloudbase, Captain Scarlet has made an amazing recovery from the dead. He has been severed from Mysteron control but retains his retro-metabolism (i.e., he is still indestructible.) We end with Colonel White explaining how Captain Scarlet will be a vital tool in the fight with the Mysterons.
(forward) Episode Two: Winged Assassin