Lord of Seagard.
Lord Jason distinguished himself in the Battle of the Trident during Robert's Rebellion, personally slaying three of Prince Rhaegar Targaryen's bannermen, and during Greyjoy's rebellion when he defended Seagard from an ironman raid and slew Rodrik Greyjoy. (AGOT 30, ACOK 12) When Ser Edmure Tully called the banners in anticipation of a Lannister incursion into the Riverlands, Lord Jason did not have a chance to join his men to Edmure before Edmure's host was destroyed, but he did join his strength to Robb Stark when he arrived. (AGOT 64) He acknowledged Robb as his king at a council at Riverrun. (AGOT 72) Soon afterwards, he returned to Seagard to defend his own lands. (ACOK 12) When Ser Edmure recalled the banners to deny Lord Tywin Lannister's attempt to cross the Red Fork of the Trident, Lord Jason repulsed several attempts by Lord Tywin's army to cross the river. (ACOK 46)