Beric Dondarrion is the Lord of Blackhaven and the head of House Dondarrion. Initially sent out by Eddard Stark to lead a party of men to apprehend Ser Gregor Clegane for atrocities committed against the people of the Riverlands, Dondarrion became leader of the outlaw resistance group known as the Brotherhood Without Banners.
Beric Dondarrion is the Lord of Blackhaven and the head of House Dondarrion, a vassal house to House Baratheon of Storm's End. He is a young lord who still enjoys the life of a knight, including taking part in tourneys. He is visiting King's Landing when the series begins.
Upon hearing of the atrocities committed by Ser Gregor Clegane, Lord Eddard Stark, acting as the Hand of the King, orders Lord Beric to take a hundred men, ride to Ser Gregor's keep and execute him for treason and murder. Beric willingly agrees to the task.
Lord Beric is rumored to have been killed in the Battle at the Mummer's Ford. The survivors form the Brotherhood Without Banners. In fact, Beric is actually killed by the Mountain, who drives a lance through his chest. Thoros of Myr unwittingly resurrects him.
Dondarrion reunites with Thoros' party at Hollow Hill, the headquarters of the Brotherhood Without Banners, and is surprised to see they have captured Sandor Clegane. Beric reveals he has converted to the religion of the Lord of Light. After Arya Stark accuses the Hound of murder, Beric sentences him to trial by combat as there is no other witness to confirm his guilt, and chooses himself as Clegane's rival.
Using magic, Beric ignites his blade with fire, initially giving him an advantage during the fight due to Sandor's fear of fire. However, Sandor's superior strength eventually proves enough to overpower Beric, and with a powerful downward swipe Sandor cuts deep into Beric shoulder, nearly cutting off his entire arm and cutting right through his flaming sword. Arya attempts to kill the Hound while he tries to extinguish his shield which had been set a flame during the fight, but she is stopped by Gendry. Sandor taunts Arya over how the gods prefer him over her friend, but he is interrupted and shocked by Beric, who has been revived and healed by Thoros using the Lord of Light's power.
Lord of Blackhaven, Beric Dondarrion arrived in King's Landing to compete in the Tournament of the Hand given in honor of Ned Stark, then Hand of the King. After Gregor Clegane terrorizes the Riverlands, Lord Beric was tasked by Ned to bring him to justice. A follower of the Lord of Light, Beric has been brought back to life several times by a red priest, Thoros of Myr. After hanging the men who raided Brother Ray's community, he offered Sandor "The Hound" Clegane a spot within the Brotherhood.