Jeor Mormont is the Lord Commander of the Night's Watch. He leads a great ranging north of the Wall to investigate rumors of wildlings amassing and White Walkers being sighted. He is killed at Craster's Keep by his own men after they rebel against the Lord Commander for not standing up to Craster.
Jeor Mormont, nicknamed The Old Bear, is the Lord Commander of the Night's Watch, leading from his headquarters at the fortress of Castle Black. Jeor Mormont was once the Lord of Bear Island and head of House Mormont until he abdicated his seat in favor of his son, Ser Jorah Mormont, and joined the Night's Watch. He rapidly rose through the ranks to become Lord Commander. His son Jorah disgraced himself by selling slaves and fled to the Free Cities, leaving Jeor's sister Maege to rule Bear Island.
Lord Commander Mormont watches the new trainees practicing and talks to Tyrion Lannister about their lack of resources. He and Maester Aemon later request that Tyrion bring word of their problems to the King and Queen and ask for their help.
Jeor conducts a ceremony to induct the new class of recruits into the Night's Watch, reminding them of the honor of their brotherhood. Jeor chooses Jon Snow, a bastard son of Lord Eddard Stark, as his personal steward. Jon thinks this an insult to his superior martial skills, but Samwell Tarly suggests that the Lord Commander made this choice to groom Jon for command.
Jeor is summoned when the bodies of Othor and Jafer Flowers are discovered north of the wall and returned to Castle Black. Sam notices that they haven't rotted, to which Jeor comments that even though Sam is a coward, he is not stupid. Later Jeor receives word via raven that Eddard has been declared a traitor and arrested. He calls for Jon and informs him of this the news, reminding him of his duty before attempting to reassure him of his sisters' safety. Later Jon attempts to stab Ser Alliser Thorne after he mocks his family for being traitors. Jeor witnesses this and confines Jon to quarters. That night Jeor enters his own quarters to find Jon fighting a Wight, Othor risen again. Jon stabs the Wight but it rises and pulls Jon's sword out of its abdomen. Jon throws Jeor's lantern on it, lighting it on fire.
Thanking Jon for his action, Mormont gives him a Valyrian steel sword, Longclaw, an heirloom of House Mormont. Jeor had previously given to his heir Ser Jorah Mormont, but Jorah had left the sword behind when he went into exile leaving Westeros in disgrace.
Jon attempts to leave Castle Black and join his brother Robb's army after he learns of Eddard's execution, but is persuaded to stay by his friends. Jeor is aware of Jon's attempted desertion but refuses to punish him, saying it is more important that he came back. Jeor tells Jon that the true danger and threat to the Seven Kingdoms comes from the White Walkers and wights beyond the Wall, not the looming civil war, and asks for Jon's help. Mormont aims to lead the Night's Watch in force beyond the Wall, find the missing Benjen Stark and identify and eliminate the threat posed by the White Walkers. Jon joins Mormont's party as it leaves Castle Black.
In the far North the great ranging of the Night's Watch traverses the Haunted Forest. They have passed six abandoned wildling villages and have been travelling for months. They reach Craster's Keep, the home of Craster, an unsavory ally who marries his daughters and has no sons. Jeor questions Craster and learns that he has not seen missing First Ranger Benjen Stark in years. Craster tells him that the wildlings are assembling under King-Beyond-the-Wall Mance Rayder. After Jon provokes Craster, Jeor aggressively reprimands him outside and confirms that he is indeed grooming him for command: he tells Jon, "You want to lead one day? Well learn how to follow."
The Watch are forced to move on when Jon follows Craster into the woods and sees him leaving a son for the White Walkers. Craster catches him and beats him. Jeor reveals to Jon that he has always known that Craster sacrificed his sons to Wildling gods but ignored it because of his value as an ally. The ranging next camps at the Fist of the First Men where they await Qhorin Halfhand and his party from The Shadow Tower. Qhorin arrives and reports sighting lookouts in the Skirling Pass. Given Mance's background as a deserter from the Watch, Qhorin predicts that the wildlings will be more organized. He suggests they accordingly shift to wildling tactics and use a small group of scouts to overcome the lookouts. Jon requests to be part of the mission and Jeor accepts with encouragement from Qhorin and a promise from Samwell Tarly that he will take on Jon's duties as a steward.
As wights and their masters descend on the Fist of the First Men, the Night's Watch are forced to try and pull back to the Wall to warn the remaining garrison of the impending attack. During the retreat Mormont saves Samwell Tarly from a wight, only to learn that he had failed to dispatch ravens requesting aid as ordered, leaving the Night's Watch to fend for itself. Mormont angrily berates Tarly for bungling his one and only task.
Mormont leads the ragged survivors of the Night's Watch expedition to Craster's Keep. Craster mocks the survivors of the Battle of the Fist of the First Men when they reach his Keep. He initially wants to refuse them shelter until he notices some of them stroking their weapons. Fearful that in desperation they might try to rush him, he relents. As the black brothers warm by his hearth, Craster mocks them. Craster insists that the black brothers should be grateful for his generosity, and that he is a "godly man" for helping them. Mormont tensely questions that he is a godly man, but Craster insists that he is - to the "real gods", the White Walkers, who consume entire armies on their way to the Wall but will spare Craster for his loyalty.
Some of the wounded men die from their injuries, and Mormont is shown giving the traditional Night's Watch eulogy as the corpse of a ranger named Bannen is burned on a pyre.
In the main hall, Mormont is checking a map in his journal, as Craster continues to crassly berate the men of the Night's Watch. Mormont says that they have to stay long enough for their wounded to recover enough to be fit to travel, but Craster waves this off, saying they've recovered as much as they ever will. Craster openly suggests that they should just kill the men who are so severely wounded that they won't be able to travel, and if Mormont is reluctant to do the deed himself, he can just leave and Craster will finish them off. Mormont declines. Another young Night's Watch man, Karl, comes in to complain that Craster is feeding them nothing but bread cut with sawdust, and he wants to know where Craster keeps his hidden larder. Meanwhile, Craster is sitting there getting quite drunk on the wine they gifted to him when they first came. Rast joins in the accusations, and Craster admits that he has winter stockpiles, but he needs those to feed his women and refuses to share them. Rast calls Craster a bastard - at which Craster becomes enraged and threatens Rast with an axe. Mormont restraints Rast, and Craster shouts that he's throwing them all out to lay down outside in the cold on their empty bellies. Craster says he will chop the hands off the next man who calls him "bastard". A tense moment of silence passes, and Mormont grabs Rast to lead him out the doorway...
...when Karl, firmly staring directly at Craster, challenges him by calling him a "daughter-fucking, wildling bastard". Craster lunges forward at Karl in a blind rage, but he is drunk and clumsy: without flinching, Karl holds off Craster's axe with his left hand, while using his right hand to ram a dagger through Craster's throat, which goes up into the roof of his mouth. He flings the dying Craster to the ground, then punches one of Craster's wives who is present, demanding to know where the hidden food is kept. Lord Commander Mormont bellows that the gods will curse him for this, as a guest killing a host who has formally accepted him into his home breaks all the laws of gods and men. Karl shouts that there are no laws beyond the Wall. Karl continues to threaten the girl with a knife, so Mormont draws his sword, which makes Karl drop the girl and begin to face off against Mormont with his dagger. As Mormont threatens to have Karl executed, Rast comes up behind Mormont and literally stabs the Lord Commander in the back, which makes Mormont drop his sword. For a brief moment the men stare in shock, then Grenn charges and tackles Karl. The entire room explodes into pure bedlam.
The desperate Night's Watch recruits like Rast, mostly conscripted criminals exiled to the Wall, turn on officers who are loyal to Mormont, as well as some of the other common recruits like Grenn who stay loyal. Quick flashes of the fight go by as no one can really perceive what's happening, and the mutiny spreads throughout Craster's Keep. In the midst of it, Mormont turns around to fight off Rast. Mormont may have a knife in his back but he is twice Rast's size and completely enraged. Mormont grabs Rast by the throat and lifts him off his feet, one-handed, then spins him around and hurls him against the opposite wall. Still choking Rast, Mormont nearly succeeds in crushing Rast's windpipe with his bare hand - but then Mormont starts to cough up thick red blood. His knife wound is mortal. The injured Mormont then sinks to the ground and continues to cough up blood. Now that Mormont is on the ground unarmed and helpless, Rast grabs a knife and repeatedly pounds it into Mormont's throat until the Old Bear is dead.
Samwell Tarly later informs Maester Aemon of Mormont's murder, and Aemon orders him to send letters all over Westeros reporting it and pleading for help. Davos Seaworth shows the letter to Stannis Baratheon, who under Melisandre's advice decides to travel to the Wall to aid the Night's Watch against any threats towards the Seven Kingdoms.
After the Mutiny at Craster's Keep, Karl and the mutineers desecrated Mormont's corpse. Karl has taken the late Lord Commander's skull as a crude cup from which to drink wine and use for his amusement.
Jon later uses Mormont's murder to persuade several of his black brothers to aid him in hunting down and killing the mutineers in order to stop them from revealing vital information to Mance Rayder. Mormont is avenged when Karl and Rast are killed by Jon and Ghost, respectively.
Jeor's dream of Jon succeeding him comes true when Jon is elected the new Lord Commander of the Night's Watch.
While travelling to Meereen, Tyrion Lannister recalls to Jorah Mormont on how he met Jeor during his trip to the Wall, and reveals that he was killed by his own men during a ranging beyond the Wall. Jorah is visibly shocked to hear of his father's murder.
During a visit to Bear Island, Jon invokes Jeor's name as he attempts to enlist his niece, Lyanna Mormont, into joining his campaign to take back Winterfell back from Ramsay Bolton.
While training to become a maester in the Citadel in Oldtown, Samwell Tarly attempts to cure Jorah Mormont of his greyscale infection, citing his respect for Jeor as a primary reason, and revealing that he was with Jeor when he died.
When Jorah is deemed fully cured of the disease, by Archmaester Ebrose, Sam says it was the least he could do due to his relationship with Jeor.
Jon makes himself known to Jorah on his arrival on Dragonstone, mentioned his stewardship under the command over Jeor.
During their trip beyond the Wall, Jorah and Jon discuss Jeor. Jon offers Jorah back the sword Longclaw, claiming that it belongs to the Mormont family. After a brief moment, however, Jorah gives the sword back to Jon, claiming that Jeor gave it to him and that Longclaw now belongs to Jon - and his children afterwards.
A grave and formidable fighter who gave his claim on his ancestral home of Bear Island to assume command of tthe Night's Watch, Mormont was known to his troops as "Old Bear". The father of the disgraced knight Jorah Mormont, he took Jon Snow under his wing t make a leader out of him. The Lord Commander was killed by one of his own men during a mutiny at Craster's Keep.