The Band of Brothers was a bandit group led by Gregor Rivers the bastard son of Randyll Frey. The group consisted of at one point 300 men who were all bastards. Gregor and his men began tormenting the Riverlands from after Gregor killed Randyll at Harrenhal. His band became known for torturing their victims, and would often put a person's eyes out after forcing them to watch something unspeakable being done to a loved one.
Brynden Frey, the lord of the Twins and Gregor's half brother, made it his personal mission to hunt down the bandits who were ravaging the small fishing villages and farmers. For nearly two months Brynden and his men tracked the Band of Brothers along the Trident. The mission and the Band of Brothers ended with Gregor's capture at a camp atop a hill in the foothills of the Mountains of the Moon. Though heavily defended the bandits were outnumbered and ill equipped compared to the Frey Lord's company.