In the original stories written by Ian Fleming, the protagonist organisation was SMERSH, a Russian intelligence organisation whose name meant 'Death to Spies'. However, it was too political to have that same organisation in films so SPECTRE was created. SPECTRE was unaligned to any government and was still headed by Ernst Stavro Blofeld, a Polish national. SPECTRE stands SPecial Executive for Counter-intelligence, Terrorism, Revenge and Extortion who is hellbent on starting World War Three.
SPECTRE features heavily in the Sean Connery and George Lazenby movies but does not appear afterwards. The exception to that is the Thunderball remake Never Say Never Again which is a non-EON Productions movie starring Sean Connery.
SPECTRE was a highly advanced organisation that had space ships at its disposal such as those that it used to capture American and Russian space craft in You Only Live Twice. In Diamonds Are Forever, SPECTRE had gotten hold of a satellite that it was using to attack nations of the world to hold them to ransom. They never quite got into actual space like Hugo Drax did with Moonraker. If they had gotten the chance , they would've.
After Diamonds Are Forever, SPECTRE disappeared from the movies due to a legal dispute between EON Productions that made the movies and Kevin McCrory who held claim to the organisations name which was not resolved until 2013. After obtaining the full rights to SPECTRE once more, EON Productions have named their 24th James Bond film after them.
The organisation had an octopus as their emblem. Although it never stood out, in the 24th film, Spectre, the emblem makes a clear return when James Bond shows a ring with the emblem on it to Mr White, the head of another organisation referred to as Quantum. Quantum is revealed to be a subsidiary faction of Spectre.
In the film SPECTRE, the organisation is still headed by Blofeld but before he reveals his 1 identity, he is referred to as Oberhauser but at his meteorite lair, he does have a white cat. The organisation is still hell bent on international incidents but at a more plausible level, the nuclear bombs have been replaced by more conventional terrorist acts with small scale bombs. The old scenes of where Spectre would hold conference meetings between its syndicates have included in the new film.