The Quartermaster is an NPC in the keep in Clan Citadels. He gives players bonus experience in a skill aligned at a skilling plot within the Clan Citadel if the player has reached level 40 in that skill.
There is no way to preview the amount of experience gained after the removal of clan rings. The bonus experience is immediately added to the skill upon selection.
He is useful for the clan that owns that Citadel to view the job list, as it shows the upkeep, upgrade and downgrade for that week and its progress.
He also changes your build tick, which is possible only by having the week's upkeep ready to be paid. You cannot change your build tick unless one week has passed since the Citadel was made.