Lyanna Mormont

Lyanna Mormont is an unseen character in Game of Thrones. She is the 10-year-old Lady of Bear Island making her head of House Mormont of Bear Island. She is the niece of Lord Commander Jeor Mormont of the Night's Watch and cousin of Ser Jorah Mormont. Her namesake is Lyanna Stark, younger sister of Lord Eddard Stark.

Biography
She is the daughter of Maege Mormont. After her mother's older brother Jeor joined the Night's Watch and later his only son Jorah fled to Essos to avoid a death sentence by Lord Eddard Stark upon being caught selling poachers into slavery to fund his wife's expensive tastes, Maege Mormont became Lady of Bear Island. Lyanna's mother is now dead, possibly during the War of Five Kings, and Lyanna has succeeded her.

Season 5
Stannis Baratheon has come to Castle Black and send ravens to all the 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. An upset Stannis offers to legitimatize him which would make him Lord of Winterfell believing that the Northerners would rally behind Jon against the Boltons. Jon admits to his friend Samwell Tarly that being a Stark was the first thing he ever remembers truly wanting, but ultimately refuses Stannis' offer as he will not violate his sworn oath to the Night's Watch.

In the books
In the A Song of Ice and Fire novels, Lyanna Mormont is the youngest of five daughters, although Lyanna is only one to remain at Bear Island during and after the War of the Five Kings. Her mother is still alive and Lady of Bear Island. When Stannis Baratheon receives Lyanna's rebuff, he is unaware who she is and ask Jon Snow about her. Jon is somewhat surprised that 10-year-old Lyanna is the one sending messages on behalf of House Mormont and he wonders if Lyanna's mother and older sisters are dead or alive.