Garon is the king of Nohr and a stern man. He is the father of Xander, Camilla, Leo, Elise, the stepfather of Azura, the husband of his first wife Katerina and the second husband of Arete, his second wife, and the paternal grandfather of Siegbert and Forrest. Following his murder of Sumeragi, he kidnapped a young Avatar and made them his adoptive child. He confined them to the Northern Fortress where they were raised alone. Due to Nohr's horrible weather and poor crop yields, he orders his children to invade Hoshido. He is ambitious and has a lust for power, and is always suspicious of others. Unfortunately his attempts to attack Hoshido were stopped by a magical barrier placed by Hoshido's queen Mikoto, which robbed any Nohrian soldier of any will to fight if they passed through it.
Several support conversations between the Nohrian siblings reveal that in his youth, he had a very different demeanor towards his children, being a doting and loving father. However, he also frequently indulged in his rather harmful passions, did not take responsibility for his actions and never could leave a woman he'd once loved. As a result, his many mistresses began jockeying for his favor, often turning to violence in the process. It's thought that this unhappy family life is what eventually hardened him into the person he is at the start of the game. Furthermore, it is also revealed that he also visited the Rainbow Sage when he was younger, and thus received power from him.
Before the events of Fates start, Garon exiled the Avatar to Northern Fortress until they were strong enough to meet his expectations. He would only let them out if they could prove themselves to him. After the Avatar bests Xander in combat, Garon allows the Avatar to return to the Nohrian capital. At the castle, Garon gives the Avatar the Ganglari and has them use it on some prisoners from a recent skirmish, including Rinkah and Kaze. After the Avatar defeats the prisoners, he then orders them to execute them, to which they refuse because they are already defeated. Angered by their refusal, he uses his magic to kill one of the prisoners. Before he can kill Kaze, the Avatar blocks it with Ganglari, angering him even more. He then orders Xander to kill them, but after a short argument and battle, Leo "kills" them instead, pleasing him before leaving to decide the Avatar's punishment.
Later on, the Avatar, along with Elise, wait outside Garon's room when they hear commotion. He is startled when he hears them at first, but after the two apologize to him for the recent event, lets them in. To make the Avatar more useful, he orders them to scout a supposedly abandoned Hoshidan fort with Hans at the Bottomless Canyon, and return when they give him a status update on it.
If the Avatar sides with Hoshido, Garon is not seen again until Chapter 12. When the Avatar and the Hoshidan army arrives in Cyrkensia to begin their assault of Nohr, they learn that King Garon was at the Opera House in hopes of seeing the famed songstress Layla. Seeing this as an opportunity to kidnap the King, the Avatar's forces have Zola disguise Azura as Layla in order to pull it off. Despite Azura's dance, which caused mild discomfort in King Garon, he reveals that he was aware of the Hoshidan Army's presence thanks to Zola. After Zola defects, he asks Garon to spare the Avatar for the kindness they showed him. Garon viewed Zola's request as a sign of treason and promptly executes him in front of the Hoshidan army and Elise who was accompanying him.
Later on, when the Hoshidan army breaks into the castle after killing Hans, he sends Iago after them to finish the job. Iago fails to kill them and is subsequently killed by Leo. After the Avatar kills Xander in a duel, the forces continue towards the throne room. Garon is "pleased" to see the Avatar again, mocking them for making it this far. Garon tells the Avatar that his family were all pawns for the war, angering the Avatar, who knows that he cannot be reasoned with, and attacks him. However, their Noble Yato is unable to penetrate his armor, and in retaliation, Garon launches several blows at them. Azura attempts to use her powers to weaken him, but Garon is well aware and grabs her, threatening to kill her unless they listen to his demands. Ryoma negotiates with him, and he responds that it is a wise choice. Garon demands that Hoshido gives unconditional surrender so its lands can be incorporated into Nohr, then stating that he wishes to kill Ryoma. Garon sends a fireball at Ryoma, wounding him.
Suddenly, Ryoma's Raijinto reacts to the Avatar's Noble Yato, empowering it into the Blazing Yato. The Avatar decides to test the new Yato on Garon, and he screams in pain, stating that it actually hurt. He calls for his soldiers to stop the Hoshidans, but they fail and the Hoshidans fight and defeat him. Garon, refusing to give up, transforms into the form of the Dusk Dragon and continues to fight, but is eventually stopped and killed by the Hoshidans. Before dying, he laments to the Avatar that he was long dead before dissipating into water. The Avatar speculates as to what exactly he means, but is unable to come to any conclusions.
Garon is shocked and angered that the Avatar had returned, knowing that they had been in Hoshido and that now know their true origins and his kidnapping of them, and agrees with Iago that they could be a Hoshidan spy and orders Xander to kill them. Xander refuses to kill his sibling, so he decides to confide with Anankos through an effigy in the ceiling. After getting his judgement on the Avatar, he sends them to the Ice Tribe Village alone to quell an impending rebellion from them. However, Xander overhears that it is an attempt to make the Avatar suffer, so he sends Silas, Elise, her retainers and their butler/maid to accompany them. They are successful in putting down the rebellion, but Iago tells Garon that the Avatar only put it down because they had allies. Upset that the Avatar disobeyed them, he nearly executes them. However, Elise and Xander tell him that it was their fault for sending help for the Avatar. Garon, while upset by their actions, is still satisfied that the Ice Tribe rebellion was put down. Giving the Avatar another chance, he sends them off to capture Notre Sagesse and crush the rebellion in Cheve. Before this, however, the Avatar reunites Garon with his stepdaughter Azura, who was kidnapped by Hoshido shortly after the kidnapping of the Avatar in retaliation. He cares little, however.
After the uprising in Cheve is put down, Garon heads to Cyrkensia and watch a performance along with his children. Before the performance starts, Garon talks to the Avatar, telling them that he is pleased with their actions on crushing the rebellion, as Hans told him. Garon is unaware that Hans had done most of the killing and not the Avatar. During the performance, a mysterious songstress uses her song to curse Garon, causing him extreme discomfort. Before the songstress could be captured, Kumagera and a band of Hoshidan soldiers arrive to assassinate Garon. After the Hoshidans are defeated and Garon recovers, he orders the Avatar to kill all the singers in Nestra. When the Avatar protests, Leo intervenes in order to prevent Garon from executing them.
Shortly afterwards, Azura reveals to the Avatar through a one-time-use crystal ball that Garon had died long ago, and that the current Garon is being possessed by "a demon" to spark the war between Nohr and Hoshido. Azura also reveals that only way for the Avatar to prove this truth to Nohr is for "Garon" to sit on the magical throne of Hoshido's Castle Shirasagi, which will reveal his degenerated slime form. This means Garon and his army will have to conquer Hoshido in order to trick him into sitting on the throne.
Garon, along with Iago, oversees the invasion of Nohr and are pleased with their progress through Hoshidan territory. After the Avatar defeats Ryoma in battle, Garon asks them to execute him. The Avatar refuses, so Ryoma commits seppuku instead to their horror. It is shown later on that Iago suggested to Garon that they should execute Ryoma. After Iago and Hans are killed, the Nohrian siblings wait outside Castle Shirasagi's throne room. When they open the doors, they find Azura's claims to be correct as the throne has revealed Garon to actually be a monster, much to the siblings' shock. "Garon" summons a group of mysterious soldiers to kill them, but they fail to do so and he is killed shortly afterwards.
Garon's true nature is hinted at in both routes during Azura's dance, where her graceful and elegant Hoshido dance only causes the monster discomfort and problems with breathing, while her aggressive and forceful dance in Conquest causes unbearable pain to Garon and his eyes to roll back.
It is revealed that the real Garon had died shortly after Elise's birth and the Garon present is a servant of the King of Valla, Anankos, who is little more than a corpse imbued with a semblance of life by Anankos' power. His mission is to destroy both the kingdoms of Nohr and Hoshido for "betraying" its master. The undead Garon makes less appearances in this route compared to the other two routes.
In his first appearance in the cutscene before Chapter 9, he is seen speaking to his stone effigy of Anankos on the ceiling, a little surprised about the fact the Avatar survived the earlier explosion at Hoshido and knowing the truth of the entire situation. He decides that the Avatar being afraid and wanting them to suffer is not enough, and that decides that the Avatar simply will have to be disposed of. He then erupts into maniacal laughter.
In his second appearance before the start of Chapter 14, Xander and Leo arrive in the throne room and see Garon looking manipulated, telling them to continue the war against Hoshido, and tells them that he wants to destroy not only Hoshido, but also Nohr itself. This causes both Xander and Leo to reconsider their earlier dismissals of the Avatar's claims about Garon being manipulated by the real culprit, the Invisible Kingdom of Valla, and they eventually join the Avatar's cause.
He makes his last appearance after Anankos' defeat in Chapter 27 of this route, offering to become a vessel for Anankos in place of Gunter, only for Anankos to eat him to reclaim the power he gifted to Garon to obtain his full power again.
Garon is portrayed as a ruthless, mean, cold-hearted man that has no mercy for anyone who does not please him or dares to defy him. He has been known to execute people on the spot without any sort of rationale, even in front of his youngest daughter. His ruthless nature extends heavily to his adopted "child", the Avatar, who is constantly ordered by Garon to perform inhuman tasks in order to "earn his trust." Actions ranging from slaughtering innocents are among the most notable, his children either reluctantly follow through with orders, or to find ways to limit the damage, but they never outright defy him. He has also expressed cold detachment to Azura, his step-daughter through his second wife, going so far as to refuse a prisoner trade between the Avatar and Azura. He has little trust even in his subordinates; though he orders Iago to kill the Avatar repeatedly, he considers him nothing more than a foolish pawn.
However, many years prior, Garon was portrayed in a different light. Leo notes that Garon would do many things typical of a loving father, such as letting Leo ride on his shoulders. While he was still a rather stern man outside of his family life, he was hurt emotionally by the deaths of his wives. Apparently, Garon was quite the ladies' man and easily won the hearts of many women, including his wives Katerina and Arete. However, his love for women prevented him from breaking their hearts, letting them do as they please, and resulted in the birth of his four children, each with different mothers. The Nohrian siblings believe that after numerous attempts by his concubines to assassinate the other children and other women to gain control of the throne, Garon became much more hardened, suspicious of any sort of trust because he felt that he could be taken advantage of if he was not careful. This perspective resulted in actions, such as beginning to antagonize the neighboring kingdom of Hoshido.
As Revelation reveals that Garon's death and manipulation by Anankos happens shortly after Elise's birth, it is in turn revealed that Garon had not gone cold due to the misdemeanors of his maidens, but rather from being under Anankos' control. This is what leads him to such actions, like ordering the death of Gunter's wife and child.
Alongside Zola, Mikoto, Hans, and Iago, Garon has unused blushing portraits within the game's code.
Garon shares many similarities with Vigarde from The Sacred Stones. Both are rulers of their kingdoms who appear to be the main antagonists of their respective games, but are later revealed to be lifeless puppets used by the true main antagonists, Anankos and Fomortiis.
Garon's model animations seem to be taken from a Knight, sharing the same idle and attacking animations; including the critical animation.
During the Birthright path, Garon's defense actually drops a point from your first encounter with him in Chapter 12 to your second encounter with him in Chapter 27
During the Final Chapter of the Birthright path, Garon will not be able to counter-attack attacks from "Spy's" weapons despite being able to in Chapters 12 and 27 as his equipped weapon has now changed to Dark Breath.
According to Fire Emblem 0 (Cipher), young Garon had a similar appearance to Xander, save for having a beard.
Also according to the Making of Fire Emblem book, Kozaki stated that younger Garon's hair was similar to Xander's.