Qyburn
A disgraced former maester stripped of his chain for experiments best not described, now a useful and unsettling servant to those who ask no questions.
A soul born at The Reach.
The fuller tale
Season Three
Introduced tending the raw stump where Jaime Lannister's hand used to be, with a bedside manner built entirely around competence rather than comfort. He was a maester once, chain stripped from his neck by the Citadel for experiments they preferred not to describe in detail, and he has clearly not stopped experimenting since. He patches Brienne up after the bear pit at Harrenhal without asking the questions a more conventional physician might, and by the time the party reaches King's Landing he has quietly made himself useful enough to Cersei that no one thinks to ask why a disgraced maester is still hanging around the Red Keep.
Season Four
Settled into the Red Keep as a kind of freelance physician to the Lannisters, useful precisely because he has no chain left to answer to and no colleagues left to disapprove. When Gregor Clegane takes a poisoned spear through the trial by combat that decides Tyrion's fate and lies dying of it in agony, Cersei brings the problem to Qyburn rather than to any maester with scruples still intact, and tells him to do whatever the work requires. He accepts without asking what 'whatever' will end up meaning, which is exactly why she picked him.
Season Five
Unveils what 'whatever it takes' turned out to mean: a silent, towering thing in Kingsguard armor that used to be Gregor Clegane and now answers only to Cersei, presented to the court as Ser Robert Strong without further explanation invited. With Varys gone east and the small council short a set of ears, Cersei hands Qyburn the spy network's remains and lets him rebuild it his own way, recruiting the city's homeless children as informants because they go unnoticed and cost almost nothing. When the Faith Militant throw Cersei in a cell, it is Qyburn, not any lord, who keeps working her release from outside the walls.
Season Six
Names Ser Robert Strong as Cersei's champion for the trial the High Sparrow has scheduled for her, a fight that never happens because Cersei solves the problem with wildfire instead of a swordsman. When the Sept of Baelor goes up and takes the Faith and half her enemies with it, Qyburn's little birds have already done their share of the groundwork, tracking who needed tracking and reporting back without ever being seen. Cersei rewards him with the small council seat outright, Master of Whisperers in title as well as function, the first time in his life anyone has handed him an honor instead of taking one away.
Season Seven
Master of Whisperers now, with a war against dragons to help plan for, which calls for tools no maester ever devised. He designs an enormous crossbow capable of driving a bolt through a dragon's eye, and gets close enough to proving it works when Bronn puts a bolt into Drogon's shoulder during Daenerys's attack on the Lannister loot train — not a kill, but closer than anyone else in the war manages. He stays close at Cersei's side through the parley in the Dragonpit, watching the Northern lords and the dragon queen agree to a peace he already assumes won't survive the winter.
Season Eight
Lines the coast and the fleet with scorpions and gets the kill this time — Rhaegal goes down into the sea on the approach to King's Landing, the single clean victory anyone manages against Daenerys's dragons in the whole war. It buys the city almost nothing; King's Landing falls anyway, and in the chaos of its burning Qyburn orders Ser Robert Strong to stay and guard Cersei rather than go looking for his brother. Gregor Clegane, who has never once in his life taken an order that mattered when a grudge was on offer, walks straight through Qyburn to get to Sandor, ending the only creature he ever fully controlled by crushing the skull of the man who built him.
How it ends for them
On the screen. Died in the Red Keep (S8·E5)
The unchained maester who built the Mountain was struck dead by his own creation — Gregor swatted his master aside on the collapsing stair when Qyburn ordered him back to the queen's side. The scorpions, the little birds, all of it ended on the stones.
The show kills him with the only instrument he ever loved. As Daenerys dismantles the Red Keep, Qyburn descends the crumbling stairs at Cersei's side, urging the Mountain to guard his queen — and when the dead Sandor Clegane appears on the stair below, the creature stops answering. Ordered to stand fast, the Mountain shrugs off his helm, and Qyburn seizes his creation's arm to repeat the command; the thing he built swats its maker aside without breaking stride, dashing him against the rubble, where he dies among the falling stones of the regime he engineered — the necromancer discarded by his own resurrection, an ending so neatly ironic it reads as the show's verdict on his whole method. In the published books Qyburn is alive and untouched, his little birds fed, his champion armored, his cellars busy.
Their chapters, book by book
A Storm of Swords 1 chapter that name them
Where the page and the screen part
The books scatter Qyburn's show duties among several players. On the page he enters at Harrenhal among the Brave Companions — the sellsword company whose butchery gave him his subjects — and his portfolio in King's Landing is narrower: necromancer-in-residence and whisperer, while the scorpions, the council theatrics and the chancellor role the show builds for him are television's consolidation, part of its general folding of the court's schemers into fewer, more visible hands. Book Qyburn's experiments are also darker for being glimpsed sideways — the cells beneath the keep, the requisitioned prisoners, the puppeteer's daughters no one mentions twice — and Ser Robert Strong is a closed helm the novels have pointedly never opened. In the published books he is alive, at the height of his influence, with his creation about to champion Cersei's trial by combat.
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.