Ser Alliser Thorne is the Master-at-Arms at Castle Black and is responsible for training new recruits to the Night's Watch.
Ser Alliser Thorne is a member of the Night's Watch. He is from House Thorne, a noble house of the Crownlands sworn to the Iron Throne. During the time of the rebellion he protected and fought for House Targaryen but was eventually defeated. Tywin Lannister gave him the choice between death or the Night's Watch. Having no choice over the matter, Ser Alliser joined the Night's Watch leaving everything he had behind. After joining the Watch, he became a ranger. During the last winter, Thorne and his ranger companions were trapped in a massive winter storm and had to resort to cannibalism to survive. Later, Thorne became the master-of-arms at Castle Black and responsible for training the new recruits.
Ser Alliser sets Jon Snow against his fellow recruits Rast, Pypar and Grenn, and mockingly refers to Jon as 'Lord Snow'. Jon beats the other recruits easily, due to his previous training at Winterfell, but is unaware that Alliser is making him unpopular by emphasizing his superiority. Tyrion Lannister advises Jon to take into account the less privileged upbringing of the other recruits and suggests that Jon could befriend them by sharing his skills.
Alliser is disgusted by the obesity and softness of new recruit Samwell Tarly, nicknaming him 'Lord Piggy'. Alliser has Rast beat Sam when he will not fight back. Jon convinces the others to refuse to hurt Sam. Alliser angrily confronts Jon and Sam, revealing that he once had to cannibalize the frozen remains of his comrades to avoid starvation during a ranging. He tells them they are soft and that Jon's 'protection' of Sam from the hard training he needs will get him killed.
Alliser is pleased when Jon is made a steward after he takes the oath of loyalty; Jon had hoped to become a ranger. Lord Commander Jeor Mormont takes Jon as his personal steward. Samwell convinces Jon that this means that Jon will be privy to the inner workings of the Night's Watch command structure, and that the Lord Commander may actually want to groom Jon for a high position within the Watch.
Alliser taunts Jon when news arrives that Jon's father Eddard Stark has been arrested as a traitor. Jon draws a knife and is punished by being restricted to his quarters. Jon redeems himself by saving Jeor Mormont's life when two dead rangers, who have been found beyond the Wall, are revived as wights. Later, the Lord Commander sends Alliser to King's Landing with the frozen hand of one of the wights to warn the court of the return of the White Walkers. He notes that part of his decision was to keep Jon and Alliser separated for a time.
Upon his return to the Wall, Thorne was declared the Acting Lord Commander of the Night's Watch. He is one of the five black brothers to "judge" Jon Snow for his actions during his time with the wildlings. Jon hides nothing of his actions, neither his murder of Qhorin Halfhand nor his affair with Ygritte. Ser Alliser disbelieves Jon's claim that the Halfhand wanted to die, but Jon counters that if Alliser was as close to Qhorin as he claims, he would know the fallen brother would have done anything to protect the Wall. Maester Aemon defends Jon on the other charge, pointing out that he isn't the first to have broken his vow of celibacy. Ser Alliser points out that Jon hasn't simply visited the whorehouse in Mole's Town: he has quite literally slept with the enemy. Jon counters with all the information that he had learned while among the Wildlings, such as Mance Rayder's strategy of attacking the Wall from the North and the South, and demands that they either kill him or let him go. Aemon tells him that they have no intention of executing him and Jon leaves. Alliser reprimands Aemon for having overruled him but Aemon wryly replies that he can tell who is lying to him, since he grew up in King's Landing.
Thorne is present when a young boy, Olly, tells the Night's Watch how a Wildling raiding party massacred his village. Most black brothers want to seek revenge and send the wildlings a message, but Thorne knows better. He knows that is exactly what the wildlings want; to draw them out of Castle Black and fight them in the open. The black brothers are interrupted by two rangers returning, Grenn and Eddison Tollett, who have escaped the mutineers holed up at Craster's Keep.
Samwell Tarly killing a White Walker with an obsidian dagger has become public knowledge among the Night's Watch. However, there are those who doubt Sam's claim, such as Thorne. Sam has earned a new demeaning nickname from Thorne: 'Sam the Slayer'.
Alliser Thorne berates Jon Snow when he sees him helping Grenn train recruits because he is a steward, and not a ranger. Janos Slynt warns Alliser that since Snow is popular amongst the Night's Watch, this will give him an edge over him when a new Lord Commander is elected. Slynt suggests sanctioning Jon Snow's expedition to Craster's Keep so the mutineers may kill Jon. The expedition to Craster's Keep is sanctioned, but Alliser tells Jon that he will not order anyone to go with him; Jon may only take volunteers. However, after an impassioned speech by Jon, a number of black brothers volunteer to go and deal with the mutineers.
Having dealt with all the mutineers at Craster's Keep, Jon and his fellow black brothers return to Castle Black. Alliser Thorne and Janos Slynt are disappointed to see Jon has survived. When Alliser catches sight of Jon's direwolf, Ghost, he orders Jon to lock up his 'wild beast' or Ghost will become food for the Watch. Later at the meeting, Jon warns the Night's Watch about the impending attack of Mance's army and suggests the tunnel to be sealed to prevent giants from bringing it down and exposing the wall. However Alliser rubbishes the claim and is seen to threaten the First Builder to disagree to the idea of sealing the tunnel. He also sends Jon and Sam to keep a watch in the night to look out for Mance's army.
When the wildling army arrives, Thorne watches from atop the Wall with Jon Snow, noting "the biggest fire the North has ever seen" and the presence of giants and mammoths. He ruefully admits they should have sealed the tunnel as Jon advised. Alliser explains that leadership means being second-guessed by everyone below you, but if you start second-guessing yourself, it is over for everyone. Alliser assures Jon they will hold out against the assault, and jokes that he and Jon can go back to hating one another when it is over.
After ordering the first volley of arrow attacks against the main wildling army, Alliser is called to bring reinforcements below to Castle Black, where the smaller wildling force south of the Wall is attacking the lightly-defended fortress. Alliser leaves command atop the Wall to the inexperienced Janos Slynt (who is promptly tricked into going below as well, leaving command on the Wall to Jon Snow) and returns to the castle. As the wildlings begin to breach Castle Black's walls, Alliser gives an inspiring speech, promising that Castle Black and the Night's Watch will still stand at daybreak, and rallies his men, personally leading the counter-charge. Alliser manages to kill several wildlings before he confronts Tormund Giantsbane on the catwalks. They duel evenly for a time, but Tormund finally manages to wound Alliser, who escapes by rolling off the catwalk and falling onto a hay-bale below. The injured Alliser is then carried to safety by two members of the Night's Watch, while screaming at the remaining men fighting to 'Hold that fucking gate!'.
Alliser Thorne has recovered from the wounds he sustained during the Battle of Castle Black and continues to observe the new recruits. As Thorne walks through the courtyard, he gives Gilly a look of contempt due to his hatred of the wildlings. Later, Thorne is present when Mance Rayder is executed by Stannis Baratheon for refusing to bend the knee.
During the choosing of the 998th Lord Commander of the Night's Watch, Alliser Thorne runs against Denys Mallister and Jon Snow. While Thorne acknowledges Jon's accomplishments, he also reminds the black brothers of Jon's sympathy towards the wildlings. However, Thorne loses by a single vote - that of Maester Aemon - and Jon is chosen as the new Lord Commander.
Stannis later advises Jon to send Alliser away to Eastwatch-by-the-Sea, but Jon prefers to keep him around in order to learn if he is plotting against him. At a meeting, Jon prepares to assign a black brother to oversee the digging of a new latrine pit. Alliser believes that Jon will use this as an opportunity to humiliate him, but is surprised and somewhat elated when Jon acknowledges his skills and names him First Ranger. When Janos Slynt subsequently defies Jon's order of reassignment, Ser Alliser initially blocks the black brothers coming to seize Janos, but ultimately steps aside. He watches with the rest of the Watch as Janos is beheaded by Jon for refusing to follow orders.
Thorne is later present when Jon departs Castle Black with Tormund for Hardhome to persuade the remaining wildlings to surrender, denouncing the mission as reckless and an insult to all the black brothers who were killed by the wildlings. He also quips to Sam that he is losing his friends, and by extension, his protection. It is possible that Thorne was in fact warning Sam about potential attacks on him and Gilly in his own, gruff way.
When Jon returns with the wildlings he managed to rescue from Hardhome, Thorne is visibly angered by the presence of wildlings outside the Wall, but gives the order to let them inside. As the wildlings are allowed through Castle Black, Thorne coldly quips to Jon that while he may have a good heart, it will get them all killed.
Thorne is part of the group that mutinies against Jon Snow by luring him outside with the promise of information about his uncle Benjen. Thorne is the first to stab Jon and say "for the Watch", as Jon realizes that he has been tricked.
Thorne does not hide his role in the mutiny and manages to win over the majority of the Watch by reasoning that Jon was willing to risk the Watch's future through his allegiance with the wildlings. Effectively acting Lord Commander of the Night's Watch once again, Thorne speaks with Davos Seaworth and offers him safe passage to the South with a horse and supplies, but Davos's mocking request for mutton convinces Thorne that they have no intention of backing down, but will fight to the death. Thorne promises Davos that if he and Jon's friends do not surrender, they will die.
After the wildlings breach the wall with the help of the giant Wun Weg Wun Dar Wun, Thorne attempts to rally the Night's Watch to fight the wildlings however they are severly outnumbered and the rest of Thorne's brothers surrender. Thorne and the other brothers who helped in Jon Snow's execution are subsequently taken as prisoners.
First Ranger of the Watch, it was Thorne who assumed temporary wartime command of the Night's Watch following the death of the Lord Commander Jeor Mormont at Crasters's Keep. Ser Allister considered himself the top candidate to repace Mormont, but lost the election to Jon Snow. Unhappy with Jon's decision to save the wildlings at Hardhome, Ser Allister conspired with his other brothers to murder the Lord Commander and was the first to attack. After Jon was resurrected by Melisandre, he executed Alliser and his co-conspirators. Thorne cursed Jon with his last words.