Lord Jason Mallister is the head of House Mallister and Lord of Seagard. He is a loyal bannerman of House Tully, and is a renowned warrior. He is an important leader in both the Greyjoy Rebellion and the War of the Five Kings. He has one known son, his heir Patrek Mallister.
He is notable for fighting in many tourneys. At the Tourney of Storm's End he is unhorsed by both Prince Rhaegar Targaryen and Ser Barristan Selmy. At the Tourney of Lannisport he is only unhorsed by the eventual champion, Lord Jorah Mormont. He is also noted for providing lavish gifts at the wedding of Lord Eddard Stark and Lady Catelyn Tully
He is noted as being an important leader during Robert's Rebellion, personally slaying three of Rhaegar Targaryen's bannermen at the Battle of the Trident, supposedly to avenge his brother. During the Greyjoy rebellion he personally slew Rodrik Greyjoy under the walls of Seagard, repelling the Ironborn fleet back into the sea.
A Game of ThronesEdit
He rides to King's Landing with his son Patrek for the Hand's Touney. He passed Catelyn Stark and Ser Rodrik Cassel on the Kingsroad, but doesn't notice or recognise them. At the tourney he defeats Ser Aron Santagar in a joust. He is identified as a threat by Ser Kevan Lannister after the outbreak of the War of the Five Kings, but Lord Tywin Lannister rejects him, claiming that he dosn't have enough men to challenge them. He captures Lord Gawen Westerling at the Battle of the Whispering Wood.
A Clash of KingsEdit
After Robb decides to send Theon Greyjoy to Pyke in an attempt to get more troops Lord Jason is dispatched back to Seagard to accompany him. During the journey Theon and Patek become close, and Jason has to remind Patrek of his house's ancient animosity towards the reavers of The Iron Islands. Lord Jason is given command of the defense of four fords at the Battle of the Fords, including the one closest to the castle of Riverrun.
A Storm of SwordsEdit
After the death of Lord Hoster Tully Jason is one of the seven elected to push off his funeral boat, as he is one of the most powerful and respected lords of The Riverlands.
It is Jason that brings news of the death of Balon Greyjoy to Robb, as well as news of the crowing of Euron Greyjoy. Lord Mallister is commanded to send two longships into The Neck to seek Greywater Watch, one commanded by Lady Maege Mormont and one by Lord Galbart Glover. Robb intends to send Catelyn to Seagard for the remainder of the war, where she will be protected by Lord Jason.
A Feast for CrowsEdit
Lord Jason surrenders Seagard to Black Walder Frey after Patrek is threatened on a gallows. He us now being kept as a prisoner in his own castle.