Ser Jasper Mormont, also known as the Great Bear, is an unseen character in Game of Thrones. He is already long dead before the events of Game of Thrones and is not expected to appear in the series. He was a notable member of Aegon V Targaryen's Kingsguard and was close friends with Trevyr Blackgard, Aegon's Hand of the King, and Ser Harlan Grayburn, a fellow Kingsguard member who also happened to be his brother-in-law. He is the father of Jeor, Maege, and Rosaline Mormont and the grandfather of Ser Jorah Mormont.
Despite being a member of the Kingsguard (who are forbidden from holding lands, taking wives, or fathering children) Ser Jasper had a family; it can be presumed that he joined the Kingsguard after the birth of his family. This was also true for Ser Harlan.
Ser Jorah Mormont tells Viserys Targaryen about his grandfather when he meets him during Daenerys Targaryen and Khal Drogo's wedding, mentioning that he had served in Viserys' grandfather's Kingsguard. His nickname is revealed to have been "the Great Bear".
While Joffrey is leafing through the Book of Brothers, he briefly stops on Ser Jasper's entry, where it is revealed that, during the War of the Ninepenny Kings, he commanded Aegon V's forces during the Siege of Tyrosh, where he personally killed "The Lord of Battles", Liomond Lashare, one of Maelys the Monstrous' advisors and leader of the sellsword company known as the Dread Legion. It is also revealed that, had he not perished at Summerhall, Aerys II would have named him the new Lord Commander of the Kingsguard. But ultimately, because of his death, this honor would go to Ser Gerold Hightower, the White Bull.