Lyanna Mormont

"Lyanna Mormont is a recurring character in the sixth season, who was previously mentioned in Season 5. She is the young Lady of Bear Island and thus the head of House Mormont of Bear Island. She is the niece of Lord Commander Jeor Mormont of the Night's Watch and first cousin of Ser Jorah Mormont."

Biography
She is the daughter of Maege Mormont. She was named after Lyanna Stark, younger sister of Lord Eddard Stark, who died years before she was born. After her mother's older brother Jeor joined the Night's Watch and his only son Jorah fled to Essos to avoid a death sentence by Lord Eddard Stark for selling poachers into slavery to fund his wife's expensive tastes, Maege Mormont became Lady of Bear Island. When Maege left to fight in the War of the Five Kings, Lyanna ruled Bear Island in her mother's stead, eventually taking Maege's place upon her death.

Season 5
Stannis Baratheon has come to Castle Black and send ravens to all the noble houses of the North with messages asking them to join his cause. Lyanna Mormont sends back a rebuff that she and Bear Island only bend the knee to House Stark. An upset Stannis shows Lyanna Mormont's message to Jon Snow which causes Jon to briefly smile and point out that, much like the Free Folk, the Northmen are loyal to their own.

Season 6
Lyanna is the first Northern leader to be visited by Jon Snow, Sansa Stark, and Davos Seaworth, who are attempting to rally the North against House Bolton. Sansa and Jon try to flatter her, but Lyanna aggressively brushes them off, demands to know why they are at Bear Island, and notes that neither Jon nor Sansa are technically even Starks, the former being a bastard and the latter being twice married. She refuses to offer her men to them until Davos steps in. He tells her that the real war is not between different houses, but between the living and the dead - and a divided North cannot hope to stand against the Night King. She agrees to help, but can only offer sixty-two fighting men. She personally leads these men when Jon travels to Stannis' old camp.

Personality
Despite her young age, Lyanna is shown to be a competent, effective, and intelligent leader, in sharp contrast to the psychotic Joffrey, timid Tommen and hyperactive Robin Arryn. While she emanates self-confidence, she does not hesitate to consult her advisors if she sees the need. As a woman and the only living heir of a major Northern house, Lyanna challenges and strives to live up to the expectations placed upon her, and behaves in a stern, no-nonsense manner when negotiating with other houses. She is extremely proud of her house, and she is devoted to protecting Bear Island's people, indicating that she views this responsibility with the utmost solemnity. Though Lyanna shares her family's fierce loyalty to House Stark, she was initially reluctant to help Jon and Sansa fight the Boltons until Ser Davos convinced her, comparing their recent rises to power and informing her of the greater threat beyond the Wall.

In the books
In the A Song of Ice and Fire novels, Lyanna Mormont is the youngest of Maege's five daughters, and the only one to remain at Bear Island during the War of the Five Kings. She is ten years old at the time King Stannis arrives in the North. In the fifth novel, Stannis sends out letters demanding the northern lords bend the knee to him. It is Lyanna who sends back a similar response as in the show, refuting his claim. Stannis has no idea who Lyanna Mormont is, and asks Jon Snow to identify her. As in the TV version, Jon says to Stannis that she is the Lady of Bear Island - though inwardly Jon thinks to himself that she actually isn't, because she has older sisters, and wonders why she would be identified as such in the letter.

Following the liberating of Deepwood Motte, however, it seems Lyanna has changed her mind about supporting Stannis, for at least one of the Mormonts - Alysane, Maege's second daughter - joins Stannis in his campaign against the Boltons.

In the novels, Maege is still alive, and was not present for the Red Wedding because Robb sent her and Galbart Glover on ahead to the Crannogmen of House Reed in the Neck, to prepare them for a push to retake Moat Cailin from the ironborn. Her whereabouts after the Red Wedding are unknown. Maege's eldest daughter Dacey was a member of Robb's personal bodyguard, however, and she was killed at the Red Wedding.