Originally there were The Four Horsemen: Death, War, Famine and Pestilence. While Death and War were controlled by seprate Gods, the Overgod created Famine and Pestilence to balance out the four. They were created from the spirit of a sick, hungry human child, and they kept part of the human spirit within them. This humanity ate away at them, making them complicated and more Human every day. They also personified the extremes of human personalities: While Pestilence was a wild risk-taking prankster, Famine was methodical and careful in everything he did.
They eventually rode out into the world, trying to find their true purpose (a humanly naive notion) by using their full powers, creating sickness and famine. The two eventually began to argue, not finishing until Pestilence stormed off in search of someone to torture. He found his target, a poor, sick woman, and was unaware as Famine crept up behind him and devoured him, absorbing his essence and spirit. The energy he spent consuming his brother drove him insane and he rode out into the forest.
11 days later, a cloaked, skinny, hunched-over figure with boils all over what could be seen of his face and body returned to the Horsemen and Gods, kneeling in front of the Overgod and declaring that he was the New Horseman, with power near that of a God, and he could be commanded only by the Overgod. He represented unity and neutrality, taking on the duties of a god of Famine and Pestilence, making sure that people were not too sick, not too healthy, not too fat and not too hungry.
The Horseman has power near that of a God and bears the responsibilities of one. He maintains his neutrality and will listen to none but the Overgod. Even then, it is speculated that he would stray from his lord in the interests of keeping any power struggle balanced and the World intact.
The Horseman's champion is a hermit who cannot become sick, hungry or old. He lives in a messy hut just outside the Sickness Pole, a "shrine" to the Horseman. Only the Hermit can go near the pole without getting terribly sick. The Horseman uses the pole to relay messages to his Champion, who in turn acts as a prophet for events like plagues, famines and so forth. The Horseman finds this often acts as a better neutraliser than a terrible sickness, and a lot less messy. The pole and surrounding areas belong to the Horseman, and he alone rules over them. He uses them for experiments, creating new kinds of illnesses or restocking them with food and wildlife for a rainy day.