1. A cult children's TV show, created by Gerry Anderson, produced by ITC and aired from 1967-1968 after the commercial flop of his flagship series Thunderbirds in the USA. Like many of Anderson's creations, Captain Scarlet's cast was made up entirely of marionettes. Unlike earlier productions though, the puppets were correctly proportioned. (no more caricature-style faces or carpet eyebrows) Also note that none of the puppets from Captain Scarlet seem to be recycled stock from other Anderson series, (see Scott Tracy from Thunderbirds and then look at Troy from Stingray) and that unlike Thunderbirds and Stingray, most of the characters have British accents as opposed to poorly-impersonated American ones.
Captain Scarlet was certainly a cutting-edge show at the time, indeed I have been told that a warning was broadcast at the beginning of each episode during the original airings, warning that Captain Scarlet has special powers and not to try any of his stunts at home. (Remind you of Power Rangers, anyone?) The show came complete with space-age (retro to us) theme music performed by The Spectrum.
In a nutshell, the show was about the war of wits between the sinister Mysterons from Mars and the special Earth military force put together to face this threat, Spectrum. (more specifically, Captain Scarlet himself)
2. Originally known as Paul Metcalfe, Captain Scarlet is the main hero in the cult Gerry Anderson children's TV program of the same name.
Captain Scarlet was just an ordinary Spectrum captain when he was sent with his colleague, Captain Brown in a Spectrum Saloon Vehicle to help co-ordinate escorting the World President to a safe location where he would be at reduced risk of attack from the newly-discovered hostile Mysterons. En-route, however, one of the tyres of the vehicle exploded, sending it hurtling over the edge of a cliff, killing both captains. The Mysteron re-generation beam was shone over the wreckage, and Mysteron re-incarnations of the pair appeared on the road, driving a seemingly unscathed Saloon Vehicle.
The shared fate of the two captains ends there, though. Captain Brown was destined to attempt to assassinate the President by exploding as he escorted him out of his office. This failed however, leaving Captain Scarlet outside as a backup, who was to try to just shoot the president and cause all manners of other evil whilst he was about it.
After much pursuit of the President's convoy, it comes down to a shoot-out between him and Captain Blue, hovering around the top of the Mile-High-Building wearing jet packs. Blue shoots Scarlet, who falls down to Earth and is knocked unconscious upon impact. (he didn't die of course because he is indestructible)
Upon waking it turns out that the impact has caused Scarlet to regain control of his mind from the Mysteron brain-programming, but has retained the retro-metabolism (ie. he cannot be killed; all his wounds will heal with time no matter how severe, although he will still experience the associated excruciating pain of the wounds) that is characteristic of all Mysterons. Additionally he gains a 'sixth sense', in that he experiences nausea and dizziness whenever he comes in close proximity of a Mysteron.
He is able to return to duty as a Spectrum officer, however his colleagues keep a close eye on him for quite some time, and his retro-metabolism is shrouded in the strongest secrecy thereafter.
Interesting note: During the time that Captain Scarlet spends as a Mysteron agent, he has one of only two face-to-face meetings with 'arch-nemesis', Captain Black, who gives him his instructions. ("You know what you must do") The only other one is when Spectrum tries to arrange a peace treaty with the Mysterons, which in fact turns out to be a trap.
My thanks to wertperch and Ashley Pomeroy for their snippets of extra information regarding the theme tune and health warning
Gerry Anderson: http://www.fanderson.org.uk