- "Look at us now, Tully! You're dead, your daughter's dead, your grandson's dead, your son spends his wedding night in a dungeon, and... I'm Lord of Riverrun!"
- ―Walder Frey, having usurped Riverrun from House Tully after betraying them.
The Lord of Riverrun is the ruler of the stronghold of Riverrun, which has been the traditional capital of the Riverlands since Aegon's Conquest. After House Tully assisted Aegon I Targaryen in a revolt against their ironborn overlords, they were made Lords Paramount of the Trident in addition to being Lords of Riverrun.
The title is held by Hoster Tully until his death of natural causes at the height of the War of the Five Kings. He was succeeded by his only son, Edmure Tully. As Edmure was unmarried at the time of Hoster's death, Catelyn Stark and Lysa Arryn were the heirs to Riverrun until a child would be born to Edmure through his arranged marriage with Roslin Frey.
Following the Red Wedding, Walder Frey imprisons Edmure and kills Catelyn, but their uncle Brynden "The Blackfish" Tully escapes and heads back to Riverrun. Walder Frey gloats that Tywin Lannister intends to reward him for the betrayal by making a Frey the new Lord of Riverrun, but it is unknown if Brynden and the surviving Tully garrison at Riverrun will accept this without a fight.
Rallying the remnants of the Tully armies still loyal to his house, Lord Brynden is able to retake Riverrun from the Freys and their Lannister allies. He takes command of the castle as the de-facto Lord of Riverrun and digs in for a siege. Lord Petyr Baelish informs Sansa Stark of this development and Sansa dispatches Brienne of Tarth and her squire Podrick Payne to secure help from the Blackfish in retaking Winterfell from Ramsay Bolton.
Embarrassed by the loss of Riverrun and facing rebellion in the Riverlands, Lord Walder orders his sons Lothar Frey and Black Walder to retake the castle. To force Lord Brynden's surrender, Walder orders them to take Lord Edmure, the rightful Lord of Riverrun, with them as hostage. Acting as de-facto Lord of Riverrun, Brynden rejects the Freys' demands and calls their bluff when Black Walder fails to carry out his threat to execute his nephew Edmure. Later, Brynden parleys with the Lannister commander Jaime Lannister and boasts that Riverrun has enough supplies to hold out for two years and that thousands of Lannisters and Freys would die for the hundreds inside his castle.
Under the auspices of Jaime, Brienne and Podrick enter the castle to parley with the Blackfish. Jaime agrees to let the Blackfish and his garrison evacuate the castle at night in order to assist Sansa and her half-brother Jon Snow. Brynden lacks the manpower to help the Starks and refuses to abandon his ancestral home. Later, Jaime convinces Edmure to end the siege by offering to spare the lives of the Tully garrison and to provide his son with a proper education. As an incentive, Jaime threatens to destroy Riverrun and catapult his son should he reject his terms. Accepting Jaime's terms, Edmure returns to the castle.
Lord Brynden tries to refuse Edmure admittance, believing it to be a Lannister ruse. However, the garrison heeds the demands of their liege Lord Edmure and admit him into the castle. Recognizing Edmure as the rightful Lord of Riverrun, they obey his orders to surrender the castle to the Lannisters and Freys. The Blackfish's protests are ignored and Edmure gives orders for his men to bind him and hand him over to the Lannisters. However, Brynden helps Brienne and Podrick to escape the castle before making a final stand against the Lannisters and Freys. Edmure is made a hostage of the Iron Throne and sent with his family to Casterly Rock.
Queen Cersei Lannister offers to install Ser Bronn of the Blackwater as Lord of Riverrun should he assassinate her brothers, Jaime and Tyrion. However, Bronn reneges on her offer, instead offering to join Jaime and Tyrion in the forces of Queen Daenerys Targaryen should he be named Lord of Highgarden.