Beric Dondarrion is a young lord and head of House Dondarrion. He is originally sent to apprehend Ser Gregor Clegane, the head of House Clegane for committing atrocities in the River lands. He is given the task by Eddard Stark, the Lord Paramount of the North and head of House Stark to act as the Hand of the King to which he willingly agrees.
He later becomes the leader of an outlaw group known as Brotherhood without Banners. When they encounter Ser Gregor Clegane in what is known as the Battle at Mummer’s Ford, it is feared that he was killed but actually survives. The survivors then form the Brotherhood without Banners. Beric is eventually killed by The Mountain (Gregor Clegane). He pierces his chest with a lance killing him instantly. He is later resurrected by Thoros of Myr, a priest in a religious order known as Lord of Light.
Beric later reunites with Thoros at Hollow Hill where he finds that they have captured The Mountain. Beric sentences Sandor to trial by combat after Arya Stark accuses him of murder at Hollow Hill. He uses magic to ignite his sword to scare Sandor, who has a fear of fire. As the match ensues, Sandor strikes Beric with his sword cutting through his flaming sword. He finds his shoulder and cuts deep into him nearly cutting his arm off. As Sandor tries to extinguish his shield from the fight, Arya attempts to kill Sandor but is stopped by Gendry, a bastard son of King Robert Baratheon (but unbeknownst to Gendry). Sandor taunts her but is shocked to see Beric alive and restored by Thoros using the power of Lord of Light. Beric is forced to set The Hound free after losing the combat.
Some of the instances where Beric has been brought back by Thoros are: being shot in the back, struck with an axe, executed by Lannister soldiers for treason, impaled with a lance and a fatal strike with a sword by the Hound.
Beric later confesses that whenever he is brought back to life by Thoros, he loses a part of him which makes him less human. He carries scars from his previous wounds like a scar on his neck from when he had been hung for treason and the missing eye which did not heal when he was brought back. He, however, does not wish the same fate for his father when he inquires from Thoros whether he is capable of bringing back a person who had been previously beheaded.