Robin Arryn
The little Lord of the Vale, a sickly, coddled boy still at his mother's breast, fond of watching bad men fly out the Moon Door.
A soul of House Arryn, born at The Eyrie.
The fuller tale
Season One
Lord of the Eyrie at somewhere around six years old, still at his mother's breast and prone to screaming fits the whole Vale is trained to indulge. His idea of justice, learned entirely from Lysa, is the Moon Door: when Catelyn Stark brings Tyrion Lannister to the Eyrie for trial, Robin spends the proceedings cheerfully asking whether the accused can fly yet. Tyrion talks and fights his way out of falling; not everyone who visits the Eyrie that year is so lucky.
Season Four
Older, marginally, but no less sheltered — until Littlefinger arrives with a niece calling herself Alayne Stone and a mother who cannot stop watching the two of them together. Robin likes the new girl more than Lysa would prefer, and it costs Lysa exactly the composure she has left: a scene in the high hall, a threat against Sansa, and then Littlefinger's hand instead of a champion's putting someone through the Moon Door. Robin is left an orphan and Lord of the Vale in truth this time, with the man who killed his mother now the only adult he has left to trust.
Season Six
Nearly grown and still hopeless with a bow, which Littlefinger — newly returned and newly indispensable — takes as an excuse to stand very close behind him and remind him whose side he should be on. Sansa arrives at the Eyrie asking for the Knights of the Vale, and it is Robin's word alongside Lord Royce's that sends them; the same boy who once wanted to watch Tyrion fly grows up just enough to help save Jon Snow's army at the last possible moment at the Battle of the Bastards.
Season Eight
A lord among lords now, one face in the crowd of Westeros's surviving great houses summoned to the Dragonpit to decide who rules them next. He has no lines that make it into the history books, but he is there — grown up, Lord of the Eyrie in more than name, watching the Seven Kingdoms get redrawn by men who once needed his word to move an army.
How it ends for them
The chronicle records no death for this soul — they are living when the tale leaves them, or their ending is a page the maesters have yet to turn.
Their chapters, book by book
Where the page and the screen part
The show gives Robin an arc — coddled wreck to fostered lordling to poised young council-voter — while the books hold him at the edge of a knife. There his fits are managed with sweetsleep, a drug that kills by accumulation; his named heir, Harrold Hardyng, is being groomed and married forward by Littlefinger with unmistakable intent; and his one protector of consequence is a girl called Alayne Stone whose real name he never learns. The book reader is invited to doubt the boy will see manhood; the show viewer watches him outlive the man who was measuring his coffin.
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.