The Double-0 designation includes the Licence to Kill, and marks the bearers as one of the top agents of British Intelligence, Mi-6. Apart from the famous Double-0 agent, James Bond alias 007, these protectors of world security remain a mystery. So, wo are these guys, the collegues of Commander Bond?
Unknown: Never appeared so far
Bill Fairbanks: killed by Francisco Scaramanga in the arms of a bellydancer in Beirut in 1969. (The Man With the Golden Gun)
Unnamed: took part in the exercise attack on Gibraltar and is captured as soon as he lands. (The Living Daylights, played by Glyn Baker. Designation in credits.)
Unnamed: killed in Siberia while smuggling a Soviet microchip. Probably married with children. (A View to a Kill, uncredited corpse.)
Unnamed: murdered by a supposed KGB assassin during an exercise on Gibraltar. (The Living Daylights, played by Frederick Warder)
Unknown: Never appeared so far in the movies. Playable as main character in a game by Sega.
Alec Trevelyan: Believed killed by Russian Colonel Ourumov during an attack on the Arkhangel chemical warfare facility in the late 80s. However, he later reappeared as head of the Janus organisation, killed by Bond. (Goldeneye, played by Sean Bean)
Bond, James Bond, Commander, Oxford graduate in languages
Unknown: Agent with whom M threatens to replace Bond in investigating Goldfinger when he thinks that Bond may turn it into a personal vendetta to avenge the murder of Jill Masterson. When it appears that Goldfinger is going to kill him with a strategically placed laser beam, Bond mentions that 008 will then take over. (Goldfinger, doesn't actually appear)
Unknown: M threatens to recall Bond from Hong Kong to undertake the assassination of General Pushkin when Bond appears unwilling. 008 doesn't know Pushkin and "follows orders, not instincts". Seems to be M's favourite back-up agent(The Living Daylights, again doesn't appear).
Unnamed: Killed by Mishka and Grishka, the knife-throwing twins in West Berlin, making a spectacular entrance to the British Embassy dressed as a clown and carrying a Fabergé egg. (Octopussy, played by Andy Bradford).
The most Double-0 agents appear in Thunderball, but are not named or in an active role. The film features a meeting in the MI-6 conference room attended by every Double-0 agent. There are nine chairs, of which Bond sits in the seventh from the right. This appears to imply that there are nine Double 0 agents at this point. None of the other agents can be seen clearly, but we see that one is bearded and another is apparently female. A similar meeting occurs in The World Is Not Enough following a bomb blast at MI-6 headquarters and the death of Sir Robert King. A group of people are briefed, including Bond. Raymond Benson's novelisation mentions that this is a group of Double 0 agents, although this is not confirmed on screen or in the credits.
In the novels by Ian Fleming, there seem to be only three Double-0 agents. In Moonraker, Bond is the most senior of those. The others are 008 (named as Bill who is resting in Berlin) and 0011 (who has been missing in Singapore for two months). The three men share an office and a secretary, in the form of Loelia Ponsonby (who was later replaced by Mary Goodnight).
008 is mentioned again in Goldfinger when it is suggested that he would replace Bond in investigating Goldfinger if 007 is killed. However, over the course of Fleming's novels there is some change in the personnel of the Double-0 section. In Thunderball 009 (now where did he come from if there were only three?) is made acting head of the section while Bond is on sick leave in Shrublands, while in On Her Majesty's Secret Service there is a reference to 006 who is an ex-Royal Marine commando.
In the novels not by Fleming, other Double 0 agents are introduced. Colonel Sun features Stuart Thomas, a Welshman who used to be 005 until an eye defect forced his retirement and who is now head of Station G (Greece). He reappears in The Facts of Death. Also in The Facts of Death M chooses to have Bond investigate the death of her lover rather than 004. 0012 is then given as the designation of the agent killed trying to retrieve Sir Robert King's money in Raymond Benson's novelisation of The World Is Not Enough.
At least in the movies, Double-0 Agents seem to have a high mortality rating, and seem to be used as plot devices similar to Star Trek's Red Shirt extras, dying to heighten the tension of the plot. The only two survivors apart from Bond seem to be the second 002, and 008, an agent that is never seen, and could as well be made up, and used by M to bring Bond into line.
Conspiracy Theory: 008 does not exist: http://www.ianfleming.org/mkkbb/magazine/agent008.shtml