Obsidian Order
The Obsidian Order was the primary intelligence agency of the Cardassian Union. One of the most ruthless and efficient organizations in the quadrant, the Obsidian Order eclipsed even the Romulan Tal Shiar in intelligence gathering and covert operations. Almost all Cardassians live in fear of the Obsidian Order, whose constant surveillance has led to the sudden eliminations of numerous "traitors". It is said that a Cardassian citizen can't sit down to a meal without each dish being duly noted and recorded by the Order. (DS9: "The Wire")
The Obsidian Order was formed in the 19th century, under the theoretical authority of the civilian Detapa Council. However, in practice it and the Central Command operated with complete autonomy. The Obsidian Order was responsible for matters of security and espionage, and was therefore forbidden from interfering in military operations. The Obsidian Order and the Central Command frequently came in conflict with each other, particularly since members of the Cardassian military are not immune to Obsidian Order inquiries. The only restriction that the Order has is that it is explicitly forbidden to possess military equipment of any kind. (DS9: "Defiant")
The organization of the Obsidian Order was separated into semi-autonomous cells, which are insulated from each other so that the capture of any particular operative has a limited ability to compromise the organization. (DS9: "When It Rains...") Certain agents of the Order are also equipped with cranial implants so that they may better resist torture. (DS9: "The Wire") They also developed a substance called promazine, which its operatives used in case of capture. (DS9: "Covenant")
In 2371, the Obsidian Order was responsible for the abduction and surgical alteration of Kira Nerys, in an operation to expose Legate Tekeny Ghemor as a sympathizer to the Cardassian dissident movement. (DS9: "Second Skin") The Order also sabotaged the USS Defiant's attempt to vaporize a silithium-laden comet headed for the Bajoran Wormhole, hoping to undermine the peace treaty between Cardassia Prime and Bajor. (DS9: "Destiny")
Also that year, the Obsidian Order was engaged in a major operation to mount a joint attack with the Tal Shiar on the Founders' homeworld. Masterminded by former Order head Enabran Tain, the Order assembled a number of warships in the Orias system, without the knowledge of the Central Command. (DS9: "Improbable Cause") The attack, however failed due to a changeling infiltrator, and the entire fleet was destroyed in an ambush by the Jem'Hadar. This failure crippled the capabilities of the Obsidian Order, essentially causing it to cease to exist. (DS9: "The Die is Cast")
With the looming threat of the Dominion, and without the Order's tight control over popular dissent, a civilian uprising overthrew the Central Command in 2372, reinstating the authority of the Detapa Council. (DS9: "The Way of the Warrior") After the Cardassian Union joined the Dominion, the Obsidian Order's role was assumed by Dominion security and the Cardassian Intelligence Bureau, who by all accounts were just as efficient. (DS9: "Rocks and Shoals")