The Obsidian Order was a secret police and intelligence organization that operated within the Cardassian Union. Its agents were widely feared by Cardassian civilians and the regular military.
Shortly before the start of the Dominion War, the Obsidian Order allied with the Romulan Tal'Shiar to launch a pre-emptive attack on the homeworld of the Founders. The entire plan was a trap orchestrated by a Founder who had infiltrated the Tal'Shiar, and the combined fleet was obliterated by the Jem'Hadar. The failed operation discredited the Obsidian Order, which virtually ceased to exist in the aftermath of the battle.