Tommen is the younger brother of late King Joffrey and Princess Myrcella, and Joffrey's heir presumptive to the Iron Throne. Though legally the son of the late King Robert Baratheon and Queen Cersei Lannister, his true father is Ser Jaime Lannister, the Queen's twin brother.
Following Joffrey's death at his wedding feast, Tommen is crowned King. His formal style is Tommen of the House Baratheon, First of His Name, King of the Andals and the First Men and Lord of the Seven Kingdoms. As he is not old enough to rule in his own right and command the military forces of the Seven Kingdoms, he does not yet bear the title of Protector of the Realm.
Tommen is presented as the youngest son of King Robert Baratheon and Queen Cersei Lannister. Cersei and Robert made a political marriage alliance after Robert took the throne by force from the Mad King Aerys II Targaryen. Tommen's real father is Jaime Lannister, his mother's twin brother. He has an older brother,Joffrey, and an older sister Myrcella with the same obfuscated parentage. Tommen is good-natured and passive in contrast to his brother Joffrey, who sometimes bullied Tommen for amusement. Like his sister, he is fond of his uncle Tyrion Lannister.
Tommen accompanies his family north to Winterfell. Tommen is eating breakfast with his mother, father and sister as his uncle Tyrion approaches. He giggles as his uncle lifts him aside to join them. His sister asks whether Bran Stark will die and Tyrion replies that he is expected to live, much to Myrcella’s delight and Cersei’s horror. Tyrion goes on to say how he wishes to see the Wall and witness the “wintry abode of the white walkers,” exciting Myrcella and Tommen. He then says he wants to urinate off the edge of it, a comment which causes both his niece and nephew to laugh. Cersei is irritated by his words and leaves, calling the children to her. Tommen attends the tournament to celebrate Eddard Stark becoming Hand of the King
Tommen attends Joffrey's nameday tournament. He is pleased when his uncle Tyrion Lannister arrives during the festivities and tells him that one day he will be as big as the Hound "but much better looking"
Tommen attends a dinner with Myrcella, his mother and Sansa Stark. He asks whether Robb will be killed after the war, and says that he wouldn't like that
Myrcella is sent to Dorne as part of a marriage pact with House Martell. Tommen watches her departure from the harbor, sobbing. Joffrey mocks him for crying. As they return to the Red Keep Tyrion senses the unrest of the smallfolk and orders Tommen sent by a separate route narrowly avoiding the Riot of King's Landing.
Tommen takes refuge in Maegor's Holdfast during the Battle of the Blackwater. Cersei takes him to the Iron Throne room when the battle seems lost. She tries to calm him with a tale about the supremacy of lions in the kingdom of beasts: the forest is full of vicious beasts, such as stags and wolves, but he is a lion, and all will bow to him. She has gotten a vial of Essence of Nightshade from Grand Maester Pycelle, which is deadly if taken in more than tiny amounts and she prepares to give it to him if the city defenses fail, to grant him the mercy of a quick death instead of being captured and tormented. She is stopped just in time when Tywin Lannister arrives to announce their victory.
Tommen is present at Joffrey's wedding ceremony to Margaery Tyrell, and during the subsequent feast (known as the Purple Wedding). Initially, he laughed at his brother's crude play with dwarves depicting the War of the Five Kings but stopped after noticing the look upon his uncle Tyrion's face. After Joffrey's poisoning and subsequent death, Tommen inherits the crown and is now the king and ruler of the Seven Kingdoms
Tommen later stands vigil with Cersei over Joffrey's corpse in the Great Sept of Baelor. Tywin, in an unusually agreeable mood, enters and proceeds to grill Tommen on the traits that make a good king, ignoring Cersei's angry glares. Tommen offers holiness, justice and strength as qualities of a good king, but Tywin refutes these ideas by pointing out that Kings Baelor, Orys, and Robert were each paragons of one of these qualities, but not very good kings. Tywin is delighted when Tommen, with minimal prompting, suggests that a good king must be wise. Tywin tells Tommen that young kings with no experience must be wise by listening to their councilors, and the wisest kings keep listening even when they don't need to anymore.
As he escorts Tommen out of the Sept, Tywin begins prepping his grandson on the duties of a king's marriage. On their way out, Jaime passes them and asks how Tommen is doing; the young king replies that he is all right.
In response to Joffrey's death, Cersei insists that Tommen be placed under high guard, with at least four Kingsguard at his bedroom door at night, something Jaime finds a bit excessive. Tommen has been moved to Joffrey's bedchamber and has yet to redecorate; hence, he has difficulty sleeping with Joffrey's gruesome hunting trophies all around. That night Margaery sneaks into Tommen's chambers. She suggests that they get to know one another before their marriage, something nobles in Westeros don't usually do. Tommen is unnerved by her presence until his cat, Ser Pounce, jumps up and Margaery interacts with him. Tommen sullenly reveals the cruel things Joffrey threatened to do to Ser Pounce, and he and Margaery bond over their mutual relief that they are free of him. Tommen agrees that he'd like Margaery to visit him again. Margaery departs, but not before giving a kiss on the forehead.
A ceremony is held in the Red Keep where the high septon officially crowns Tommen as king. Margaery watches from the side, and, when questioned by Cersei, notes that he sits as comfortably in the Iron Throne as if he were born to it. Cersei and Tywin later set the date of Tommen's wedding to Margaery immediately after the mourning period for Joffrey is over: a fortnight from the day of the coronation.
On Tywin's instructions, Tommen recuses himself from presiding over Tyrion's trial for Joffrey's murder, declaring Tywin, as Hand of the King and Protector of the Realm, as his replacement. He then departs the throne room along with two Kingsguard.
During the wake of his grandfather, Tommen is approached by Margaery, who shares a few close words with the king and holds his hand briefly. All of this is observed by Cersei from afar.
Claiming to be acting under Tommen's orders, Cersei convenes a meeting of the Small Council, declaring that Tommen has decided to wait until he's older to appoint his own Hand of the King. She also invokes Tommen's name in appointing Mace Tyrell the new Master of Coin as well as the Master of Ships, in promoting Qyburn to Master of Whisperers, and in offering Kevan Lannister the new position of Master of War. Kevan calls Cersei out however, and refuses to serve unless Tommen himself asks him to.
Tommen and Margaery are finally married, to much fanfare. They waste little time in consummating the marriage, although it seems to go rather quickly. Tommen muses that his mother doesn't like King's Landing, and Margaery subtly implies that Cersei, will continue acting like a mother lioness around Tommen in spite of the fact that he's reached his majority and is now married. The following morning, Tommen walks with his mother on the battlements and suggests that she might go back to Casterly Rock, since she's always described it as home. Cersei denies this, saying that King's Landing is her home. When Cersei later talks to Margaery, she finds the younger queen bragging about Tommen's libido, which she says is to be expected, given that he's both a lion and a stag.
After Margaery's brother, Loras Tyrell, is arrested by the Faith Militant for his homosexuality, Tommen is confronted by an angry Margaery, who tells him that Cersei was most likely behind this to separate them. Tommen confronts his mother and demands that Loras be released, but she calmly tells him that she did not give the order, but it was the High Sparrow, although Tommen still blames Cersei for giving the High Sparrow an army in the first place. Tommen later goes to the Sept of Baelor to try and speak with the High Sparrow, but the Sparrows block his way. His Kingsguard offer to fight their way through the crowd to get inside, but Tommen refuses to allow bloodshed, even when he himself is insulted by the common folk as a "bastard" and an "abomination". He later regretfully tells his wife that he was unsuccessful.
Tommen is present when Margaery gets arrested, though he is too stunned to do anything, despite Margaery's desperate pleas.
Later, he voices his frustration and his plans to attack the Sept of Baelor in front of his mother, who manipulates him into letting her handle the situation. When this eventually leads to her capture by the Sparrows, however, Tommen loses his appetite and falls into depression, refusing to eat and staying in his chambers, receiving no one. Tommen later takes a holy vow of silence, swearing not to speak until all of his enemies were destroyed.
Worried that his mother would be rearrested should she set foot in the Great Sept of Baelor for his sister's wake, Tommen has Cersei confined within the Red Keep for her perceived safety, to her unseen anger. When confronted by his uncle, Tommen told him that he felt his mother was somehow responsible for Prince Trystane's murder, but was no longer upset with her, despite knowing she re-armed the Faith Militant. Jaime chastised his nephew for this very action; himself irate over his sister not being able to see her daughter in the Sept. Right before encountering the High Sparrow, Jaime tells Tommen to head to the Red Keep and apologize to Cersei, which he does soon after. Upon seeing his mother, Tommen tearfully apologized for his earlier command and wished he was tougher in order to deal with those that would wrong him; especially in light of his earlier humiliation when he failed to force the Faith Militant to release his brother-in-law as well as his inability to fight for his queen upon her arrest. Cersei readily accepted his apology and offered her son help in gaining his desired power and effectiveness.
Later, Tommen and his Kingsguard visit the High Sparrow to seek permission for his mother Cersei to visit Myrcella's crypt at the Great Sept of Baelor. The High Sparrow denies Tommen's request on the grounds that his mother has not been cleared of the other crimes, namely killing King Robert Baratheon and incest. Tommen criticizes the Sparrow for his harsh treatment of Cersei when she has already atoned for her other two crimes: falsehood and fornication. In response, the High Sparrow compliments Tommen for his deep love to his mother, which he attributes to The Mother, one of the seven manifestations of The Seven. When Tommen questions why the Sparrow wants to punish his mother, the latter replies that he is merely carrying out the will of The Seven. The High Sparrow urges Tommen to turn to The Seven for wisdom. Before Tommen leaves, he tells the King that the Seven have worked through his grandfather and mother even though they may not have acknowledged it.
Later, Tommen is briefed by Grand Maester Pycelle who advises him to accomodate the High Sparrow. His mother Cersei walks in on the briefing and asks Pycelle to leave under the pretext of asking her son about the latest Small Council meeting. During their conversation, Tommen proposes that the Iron Throne not antagonize the High Sparrow in order to safeguard his wife and Queen, Margaery Tyrell. Cersei then reminds her son about her humiliation at the hands of the Sparrow. Exploiting Tommen's love for Margaery, she tells her son that the Sparrow has no respect for kings, queens, and society. Tommen then tells her a secret that the High Sparrow had told him not to share with anyone else: that the Sparrow is planning to make Margaery do the Walk of atonement
The High Sparrow later allows Tommen to speak with Margaery. He reassures her the crowds would go easy on his wife since Margaery is popular with the people. In her cell, Margaery speaks positively of the Sparrow and expresses contriteness for her "sins." Tommen finds himself agreeing with her assessment of the Sparrow and decides to convert to the Faith of the Seven. When his "uncle" Jaime Lannister leads a Tyrell show of force outside the Great Sept of Baelor, Tommen and his Kingsguard exit the doors of the temple under the Sparrow's signal. The Sparrow announces to the crowd that Margaery will not have to make the Walk because she has brought another to the Faith. Addressing the crowd, Tommen announces that the Crown and the Faith are the two pillars that hold up the realm. As a symbolic gesture, he and Margaery raise their hands to the applause of the crowd. Later, Tommen strips Jaime of his position as Lord Commander of the Kingsguard for "attacking the Faith and the Crown." He then places his uncle in charge of a Lannister army sent to help the Frey lay siege to Riverrun, which has been retaken by the Tullys
During a royal announcement, King Tommen announces that the Crown and the Faith are the two pillars that hold up the world. He adds that all those who break the law will be judged by the Father. After consultations with the Faith, Tommen also abolishes trial by combat, denouncing it as a barbaric practice that has allowed corrupt rulers and lords to evade justice. He adds that his mother Cersei and Loras Tyrell will be tried before seven Septons as it was in the "old days." The trial would take place at the Great Sept on the first day of the festival of The Mother.
Having watched the Sept of Baelor explode, Tommen knows that his wife is dead. Unable to cope with the grief of the tragedy of his wife's death and the explosion, he jumps from his window in the Red Keep
The youngest of Robert and Cersei's children, Tommen inherited the throne after the death of his brother Joffrey. He married his brother's widow, Margaery Tyrell, whom he loved. Gentle and kind-hearted, Tommen failed to help his mother and wife after they were imprisoned by the Faith Militant. When he learned Margaery died in the explosion in the Sept of Baelor, which his mother caused, Tommen killed himself.
Tommen is kind-hearted, considerably quick at assessing situations and has a strong emotional side. Even as a young boy, Tommen’s kindness becomes apparent when he states his distaste at the possibility of Robb Stark being killed, even though they’re on opposite sides. His considerate side is seen when he initially chuckles at the mocking of the War of the Five Kings performed by dwarfs at the Purple Wedding, but stops when he realizes it is a mockery of his uncle Tyrion. Tommen is quite quick at grasping things and he realizes that a good king needs to be wise, much to his grandfather Tywin's delight. He is also a great deal more pensive than his brother Joffrey, who was prone to needless brutal violence. This is illustrated when the Faith Militant bar him from Baelor's Great Sept and his Kingsguard want to attack them. As they are in full view of the people, Tommen orders his men to stand down and forbids them from attacking.
His kind heart, however, also is a weakness, as it allows him to be manipulated easily by others, especially by his wife and his mother. Moreover, his emotions occasionally take over, causing him to react very emotionally at times: he is beside himself with grief and anger when Margaery is arrested by the Faith Militant and he is powerless to help her. Later on, when he learns his mother has also been arrested, he goes on a hunger strike.
Tommen is on good terms with his entire family, with the exception of Joffrey, whom he feared greatly. He is also one of the few members of House Lannister who has a loving relationship with Tyrion. He is closest to his sister Myrcella, likely because they were both abused by Joffrey and largely ignored by their parents, and is as such very shaken when she departs for Dorne.