The Brotherhood Without Banners are the survivors of the group sent out by Lord Eddard Stark to bring justice to Ser Gregor Clegane after he starts to ravage The Riverlands. They are ambushed at the Battle at the Mummer's Ford and the survivors unite after the death of King Robert Baratheon,staying loyal to him and swearing to protect the smallfolk during the War of the Five Kings.
The Brotherhood are initially led by Lord Beric Dondarrion and Thoros of Myr. Beric dies numerous times but, through the red god, Thoros continuously brings him back. The Brotherhood starts to attract more members after other battles occur, including the Tyroshi sellsword Greenbeard and the intimidating warrior Lem Lemoncloak. They target both Wolves and Lions alike, and many villages and towns are sympathetic to the Brotherhood, such as Stoney Sept.
A Clash of KingsEdit
At some point the House Lannister forces under Ser Gregor Clegane are tasked with rooting out and destroying the Brotherhood. he routinely catches members of villages he thinks may be sympathetic to them so that his men can torture them into giving information. Arya Stark is captured by one such group, and she is taken to Harrenhal, where Gendry is almost tortured to death by the Tickler.
A Storm of SwordsEdit
After escaping Harrenhal with Gendry and Hot Pie Arya is seized by Lem, Tom of Sevenstreams and Anguy, three members of the Brotherhood. She is then taken to an inn where she meets Greenbeard and Harwin, a former guard of Winterfell. Harwin identifies her as Arya, and the group decide to take her before the Lightning Lord, Beric.
Whilst at Stoney Sept the brotherhood take control of Sandor Clegane, who had been captured by the Mad Huntsman. Sandor is given a trial of combat by Beric, who uses a flaming sword. Sandor manages to win and is set free. He is stripped of his money, however, and the Huntsman and greenbeard are sent to The Reach to acquire grain that is much needed by the people of the Riverlands.
At some point after the Red Wedding the brotherhood come across the corpse of Catelyn Stark in the Trident. Thoros refuses Harwin's plea to revive her, but Beric accepts and gives his own life to bring her back. After this the Brotherhood switches command to Catelyn Stark, who adopts the name Lady Stoneheart and launches a vengeful campaign against House Frey, House Lannister and House Bolton. They hang Petyr Frey, who is fourth in line to the Lordship of the Crossing as well as Merrett Frey, who had been sent to ransom Petyr.
A Feast for CrowsEdit
The Brotherhood is now fully under the control of Stoneheart, and this has caused some of it's members to leave, as they do not agree with her motives or methods. Anguy and Edric Dayne, for instance, leave after Beric's final death.
The Brotherhood continues their campaign of vengeance when, after he is dismissed from the Siege of Riverrun, Ser Ryman Frey is ambushed and hanged, along with the rest of his party. Ser Ryman had been the heir to the Twins at the time. Although the Brotherhood committed the act, Edwyn Frey believes that his brother, Black Walder Frey, was involved in the act, to strengthen his claim on the Twins.
Shortly after this event Brienne of Tarth runs into members of the Brotherhood, including Gendry, who saves her life by killing Biter, and Lem, who takes her, Podrick Payne and Ser Hyle Hunt prisoner, bringing them before Lady Stoneheart, who accuses Brienne of forgetting her oath and siding with House Lannister. she gives Brienne the choice of being hanged or finding and killing Ser Jaime Lannister to prove her loyalty.