In the mirror universe, the Obsidian Order was the former intelligence and covert operations agency of Cardassia, charged with helping to maintain the security of the Klingon-Cardassian Alliance. Like their "primary" universe counterpart, the Order routinely monitored Cardassians, and via Cardassia's membership in the Alliance, influenced a large portion of the Alpha and Beta Quadrants. The Order employed many non-Cardassian agents to facilitate this control, including spies (some surgically altered) and mercenaries, among them Neria April and her mother, Ilona of Khalindar.
The Obsidian Order posed a significant threat to the Terran rebellion against the Alliance in the 2370s, until the Overlords destroyed and eliminated them. By 2385 the Obsidian Order was defunct. (Star Trek: New Empire)