Emblem of the Breen Confederacy.
The Domo of the Breen Confederacy is the Breen head of state and head of government. (ST - Destiny novel: Mere Mortals)
In 2381, the Breen Domo condemned Federation President Nanietta Bacco's "compulsory summit" of various foreign ambassadors to the Federation to gain support for the Federation's war with the Borg Collective as an insult to his people's sovereignty. (ST - Destiny novel: Mere Mortals)
In 2382, Brex was Domo. He authorised Thots Keer and Naaz (the leaders of the production of the Breen slipstream vessel Marjat and the Breen Militia's Special Research Division respectively) to use any means necessary to complete the construction by a deadline, including kidnapping citizens. (ST - Typhon Pact novel: Zero Sum Game)
In 2384, Brex was given a vote of no confidence due to a failed mission which resulted in the loss of two of the Breen's top cyberneticists, millions of sakto and the sacrifice of an entire intelligence operation. Brex was expected to be replaced by Pran. (TNG - Cold Equations novel: Silent Weapons)