At the age of four and ten, Halfjon realized that he would get nothing in terms of birthright and claims from his father or The Last Hearth, so he traveled south with his brother. He ended up enlisting in several Tourneys throughout the Riverlands and The Reach. During the Tourney at Castle Darry at the age of six and ten, Halfjon won the melee. Damon Lannister recalls being unseated by a young, plainly armored Jon Umber during this tourney as well.
He joined King Harys Baratheon's Kingsguard in the year 499 AC.
Halfjon fought alongside King Harys Baratheon during the Ascent of the Lion, and died during the final battle of the Kingswood.
"Some jumped-up Northman, half as much direwolf as giant." - Loren Lannister describing Jon
Brandon Umber, father (deceased)
Forrest Umber, brother (deceased)