Dagos is the Marshall of Baator's armies, a member of the Dark Eight. Dagos is in charge of the Ministry of Strategy for the Blood War on the Baatezu side. He's the only one that actually acts as a traditional general, leading the nine baatezu generals in the Blood War and sharply disciplining them.
Bel was formally subordinate to Dagos; his title was chief general of the Third Command. When he orchestrated his coup against Zariel with the aid of the Sign of One faction, Asmodeus did not let him off the hook. He still must report to Dagos, and Dagos can still give him orders with regard to his prosecution of the Blood War. Bel's layer, Avernus, is his to command alone; the Dark Eight's authority does not extend to the administration of the layers of Baator.
The other generals of the Third Command are Meritos and Hanariel, both gelugons. The Third Command mostly commands lemures, nupperibos, abishai, and other minor devils.
The Second Command is the baatezu navy, in charge of aquatic combat and Styx transport. Their generals are Kobbis (an animzu), Meathe (an amnizu), and Laginus (a cornugon).
The First Command is the elite troops, the special forces. They are made up of extremely powerful baatezu and go on extremely hazardous missions. Their generals are the pit fiends Alusiel, Phanior, and Galarond.