The Broken Legion is its own infamous regiment talked about with scorn throughout the Cabal forces. Valus Trau'ug disobeyed a direct order from Cabal High Command to not attack the Reef, yet he gathered his loyal supporters and attacked anyway. He was easily apprehended by the Awoken and locked in the Prison of Elders. Urrox commanded the Cult of the Worm. They were his personal brood, like the Spawn of Crota are to Crota and the Blood of Oryx are to Oryx. Urrox is a descendant of Crota, being somewhat of a demigod. The Cult of the Worm is a long-forgotten brood that has been nearly vanquished. They most likely found the other side of the keyhole and entered the Abyss. From there they could be transmatted out by their Ghosts