Hammar was the Gaidin Blademaster in the White Tower, in charge of training aspiring Warders in swordplay. He was a Blademaster and by right, owner of a Heron-marked sword. It has been stated that he must have respected Siuan Sanche very highly, due to his decisions that led to his death.
He was said to be solid and shaped like a block of stone, with a gravelly voice to match.
He required Galadedrid Damodred and Gawyn Trakand to fight Matrim Cauthon, still weak from his ordeal with the ruby-hilted dagger, and who was armed solely with a quarterstaff to their two swords, to teach them a lesson on combat.