The Stalliarch Lords, also known as the Once-Noble, the Merciless Riders, and the Equumorti, are an Ossiarch Legion renowned for both their thunderous mounted assault and their twisted code of honour. Hailing from the dead found in the Horseman's Paradise of Equuis Main, the Lords believe themselves to be great and noble warriors. But this is untrue; indeed, they are as twisted by Nagash's cruelty as any other Legion. 
This is demonstrated by the way they gather bones for the Tithe; usually, a a lone rider in the dead of night will travel to a settlement and issue a challenge. Whilst the challenge itself may differ from attack to attack, it will always be almost impossible. Known challenges have been providing a tonne of exhumed bone per capita overnight, or recounting the full lineage of everyone in the city since it's inception, or even forcing the best rider in the settlement to duel with the elite rider; it matters not. When the challenger inevitably fails, in the eyes of the Stalliarchs, the lives of everyone in the settlement is forfeit. 
Shortly afterwards, the settlement will be razed by the Lords, their honour satisfied. It matters not to them whether the challenge is irrelevant, for in their minds if the prey is given a way out and still fails, be it on their head. 
The Lords make heavy use of Kavalos Deathriders, riding them down with a cold joy. They are, after all, the most vital of the Ossiarch Legions, an aspect reinforced by their gory and blood-flecked appearances. Should the Tithe not be met, the offenders will be ridden down in a series of brutal assaults, spear and sabre slick with gore. Actions such as these truly show their psychopathic disregard for mortal life.