Lyanna Mormont
The child Lady of Bear Island, all of ten years old and fiercer than lords five times her age, who suffers no condescension whatsoever.
A soul born at Bear Island, sworn to House Mormont.
The fuller tale
Season Six
Not yet a teenager, and already Lady of Bear Island, and the only northern lord who does not blink when Jon Snow and Sansa Stark come asking for swords. She hears Jon out, tells him Bear Island's men are needed at home, and sends him off with sixty-two of them anyway — more than he expected, less than he wanted. After the Boltons fall she stands up in a hall full of grown men who waited to see who would win before picking a side, and shames every one of them into kneeling; Jon becomes King in the North because a child spoke first.
Season Seven
Still the smallest voice in the room and still the one nobody interrupts twice. She sits on Sansa's council as Winterfell braces for winter, wary of promises made by southern queens and impatient with anyone who treats her age as a reason to leave. When word comes that Jon has bent the knee to Daenerys Targaryen in the south, she says what half the hall is thinking — that he was their king, crowned by their own lords, and has given it away without asking them — before the argument moves past her and the North holds together regardless.
Season Eight
Lady of Bear Island in a castle full of strangers, unimpressed by dragons, Dothraki, or Tormund Giantsbane's stories about the far north, and as blunt as ever about what Bear Island can still spare for the fight. In the dark of the Long Night a wight giant sweeps her off her feet, and dying in its fist she drives a dragonglass blade through its eye — a kill nobody twice her size manages that night, and the reason Bear Island's name is said with something more than pity afterward.
How it ends for them
On the screen. Fell in the Long Night (S8·E3)
The little bear of Bear Island, ten years old and fiercer than her whole hall, was seized by an undead giant in Winterfell's yard. Crushed in its fist, she drove her dragonglass into its eye with her last strength and killed it as it killed her.
Lyanna Mormont fell in the Long Night, in the battle for Winterfell against the dead — and her death is the battle's defining miniature. When an undead giant smashes through the castle's gate and begins swatting defenders aside, the smallest person in the yard charges it, screaming, dragonglass in her fist. The giant catches her, lifts her, and crushes her in its grip — and Lyanna, dying in its fist, drives her obsidian dagger into its eye and kills it as it kills her. She trades herself for a giant at ten years old, the best exchange rate any soldier achieves in the whole war; the wight that rises briefly from her afterward is put down by others, and the North's memory keeps the first version. In the books she is alive on Bear Island, her letter written, her legend not yet required.
Their chapters, book by book
Where the page and the screen part
In the books, Lyanna Mormont is a single glorious sentence: the ten-year-old whose letter about the King in the North, whose name is STARK, is read aloud in Stannis's camp — and everything else about her is the show, which took the letter, gave it a face, and built a fan-favorite from the extrapolation. Book Lyanna is alive on Bear Island, youngest of five Mormont sisters in a succession the books track carefully; the show simplified the family to put the island directly in her small hands. She is the adaptation's best case study in expansion rather than invention: three scenes grown faithfully from one line of ink.
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.