Beric Dondarrion
A lord of the Marches sent to bring the king's justice to the Riverlands, who became instead the outlaw leader of the smallfolk's own brotherhood.
A soul born at Blackhaven, sworn to The Brotherhood Without Banners.
The fuller tale
Season One
Sitting the throne, Ned sends Beric Dondarrion to bring the Mountain's head and summons Tywin to court.
Where they stand. King's Landing.
Season Three
Leader of the Brotherhood without Banners, and already a dead man several times over by the time Arya meets him — Thoros has pulled him back from the Lord of Light's fire again and again, and neither of them can fully explain why it keeps working. He puts Sandor Clegane on trial for the butcher's boy's murder and settles it the outlaw way, trial by combat, and loses: the Hound's sword finds him before his own burning blade does any good, and Thoros kneels over the body and prays him back once more, nobody bothering to count which time it is anymore. The cause needs gold more than it needs prisoners, so Gendry goes to Melisandre for a purse of gold dragons, over Arya's furious objections, and the Brotherhood rides on without him.
Season Six
Years gone from the story and reappears exactly when the Hound needs him — Beric and Thoros arrive with the remnant of the Brotherhood in time to cut down the marauders who hanged the villagers Clegane had tried to help, the same men, more or less, who used to ride under Beric's own banner before they slipped off to plunder in his name. Over the fire afterward he tells Clegane plainly what he told Arya once and will tell others eventually: the Lord of Light keeps returning him for a purpose he still cannot name, and something is coming from beyond the Wall worth living to fight. He asks the Hound to ride north with them instead of chasing his own revenge, and the Hound, against his own habits, agrees.
Season Seven
North of the Wall with Jon Snow's ragged company to catch a wight and drag it south as proof — Beric, the Hound, Jorah, Tormund and the rest, walking into country that used to be a story wildlings told to frighten children. When the dead surround them on a frozen lake he's the one who lights his sword and holds the line, and the flame is the only thing keeping a wight bear off the Hound long enough to matter. Trapped through the night on a rock as the Night King's army closes in, he lives to see Daenerys arrive on dragonback to pull them out — and watches the Night King bring Viserion down out of the sky with a spear of ice, proof, if the chained wight wasn't proof enough, that the stories were never just stories.
Season Eight
Held over for one more purpose, and the Battle of Winterfell provides it. Cut off with the Hound and Arya in the castle's covered walkways as the dead pour through the breach, he throws himself at the wights again and again with nothing left in him but the fire on his sword, buying the seconds Arya needs to keep moving toward the godswood. It finally takes; the Lord of Light doesn't call him back this time, and the Hound, kneeling over him after, understands only then what all those resurrections were actually for — not Beric's war at all, but getting a girl with a dagger to the right room at the right hour.
How it ends for them
On the screen. Fell in the Long Night (S8·E3)
The Lord of Light's oft-returned knight spent his last resurrection the way the god apparently always intended: holding a corridor of wights off Arya Stark's back. The flaming sword went out for good, purpose served.
On the page. Gave his last life at the Trident (ASOS, ch. 82)
Six times the flame of R'hllor pulled the lightning lord back from death, each return leaving less of the man. At the Trident he spent the last of it, mouth to mouth, on a three-days-drowned corpse the brotherhood pulled from the river. What rose was Lady Stoneheart.
In the books Beric dies for the seventh and last time at the Trident, and no part of it is in battle. The Brotherhood pulls a woman's three-days-drowned corpse from the river — Catelyn Stark, thrown to the water after the Red Wedding — and Beric gives her the kiss of fire that Thoros cannot bring himself to attempt, passing the flame that has kept him walking into her. He stays dead; what rises is Lady Stoneheart, and the Brotherhood that follows her is his kindly court of the hollow hill curdled into a hanging judge. In the show he spends his last resurrection at Winterfell during the Long Night, taking wound after wound in a torchlit corridor to wall the dead off Arya Stark's retreat — and when Melisandre says the Lord brought him back for a purpose now served, the story, for once, has no rebuttal: the girl he died shielding ends the Night King within the hour.
Their chapters, book by book
A Game of Thrones 1 chapter that name them
A Storm of Swords 1 chapter that name them
Where the page and the screen part
The show's Brotherhood is a band of likable rogues; the books' is a tragedy in institutional form — founded on a dead king's justice, slowly corrupted after its founder's final gift into something that hangs first and tries never, under a leader the show chose not to create. That choice is the great divergence: book Beric's ending is inseparable from Lady Stoneheart, and cutting her rewired his entire meaning — the show's Beric becomes an instrument of the Lord of Light's long game against the dead, while the books' Beric is a cautionary miracle, proof that what comes back is never all of what went in. The show also softens the Brotherhood's low point: selling Gendry to Melisandre is its invention, book readers note, and rather against the books' Beric's character — though the books' Brotherhood ends up somewhere worse.
Their journey
Where the two tellings send them to the same place the road runs whole; where they part, the screen keeps the left and the books the right.