The Brotherhood was an organization that operated in the Cardassian Union.
The Brotherhood's members were elite aristocratic and military Cardassian families, including the Dukat and Lokar families. While the Brotherhood claimed to be a friendly organization that engaged in sporting and social events, they actually plotted against the Civilian Assembly to increase the power of the Cardassian Central Command. The Brotherhood was also dedicated to removing members of the military they saw as traitors to Cardassia and also pushed for war against the Klingons and the United Federation of Planets.
In the 2360s, Enabran Tain assigned Elim Garak and Pythas Lok to gather evidence of the Brotherhood's subversive activities that they could take to the Detapa Council and the Civilian Assembly to discredit the Brotherhood and Procal Dukat. Lok went undercover as Tonarkin Bine, an experienced forest guide, and gained a position organising the Brotherhood's recreational activities. Procal Dukat was kidnapped and interrogated by Garak, although he did not reveal any names of the Brotherhood's members to Garak. (DS9 novel: A Stitch in Time)