Jon Umber son of Umber

When Robb Stark calls his father's bannermen, the Greatjon comes with his men, but he does not simply bend the knee: he demands an honored place in the fighting and threatens to march back to Last Hearth if he is refused it. He draws his sword in front of everyone, and Grey Wind tears it from his grip, taking two fingers with it.

Far from shaming him, the episode convinces him that Eddard Stark's son has the makings of a leader, and from then on he backs him without question. When the northern host splits at the Twins, the Greatjon marches south at the head of the vanguard, fights at the Whispering Wood and at the Battle of the Camps, and sets fire to the siege towers Jaime Lannister had raised outside Riverrun.

When the siege of Riverrun is lifted and word arrives of Lord Eddard Stark's death, he is the first to raise his voice: "This is the only king I mean to bend my knee to, my lords. The King in the North!"

At Riverrun, the Greatjon listens as Robb lays out before his council the terms he offers the Iron Throne. He then fights at the Battle of Oxcross and takes part in seizing the gold mines of Castamere, House Reyne's old seat, along with Nunn's Deep and the Pendric Hills.

When Robb breaks the betrothal that bound him to a daughter of House Frey, the Greatjon offers his own uncle to stand at the altar in the king's place, so as not to break the pact with the lords of the Twins entirely.

He leads the vanguard on the march to Lord Edmure Tully's wedding, and is given that same command again in Robb's plan to seize Moat Cailin from the ironborn.

At Edmure Tully's wedding, the Freys tasked with getting the Greatjon too drunk to fight —Petyr, Merrett and Ser Whalen— do not quite manage it. When the killing starts it takes eight men to bring him down: before he falls he kills one, wounds two more, and bites off half of Ser Leslyn Haigh's ear.

After the massacre, the Greatjon survives, but ends up a prisoner of House Frey, held at the Twins with little known of his fate.

While the Greatjon remains a captive, his forces in the North split. One part, led by his uncle Hother Umber, swears grudging loyalty to House Bolton, though Roose Bolton does not trust that oath very far. The other, led by Mors Umber, throws in with Stannis Baratheon.