The Hunt and Old YharnamThe residents of Yharnam are familiar with the tradition of the hunt. When the moon comes close, the most blood-addled become beasts, and doors are closed for the night as hunters sweep the streets and slaughter their prey.
Gehrman was the first hunter, and the host of the Hunter's Dream, but we'll return to him later. What matters historically is that he inspired other hunters, some of whom followed his methods and some of whom diverged. The Healing Church had its own line of hunters, began by Ludwig, a necessity because as the most blood-addled citizens of all, clerics would turn into the most hideous beasts. It even began to create special blood gems for the task.
Known as Old Yharnam in the game's timeframe, the first Yharnam was afflicted with what was called 'ashen blood.' Everyone began to turn and the Church could find no cure, only mild delaying tactics. It sent in a splinter group of the hunters, the Powderkegs, known for their combustible problem-solving. The Powderkegs burned the town to cinders, stayed behind to slaughter any survivors, and in this horrific process either died or abandoned their hunter's vows. The Church, meanwhile, abandoned Old Yharnam to this fate, and sealed it off from the rest of the city.
This was a mere hint of what was to come. There is an interesting suggestion that the beasts began to overwhelm the hunters, because Ludwig started to recruit normal people to join the hunts – few of whom would survive the experience.
As this suggests, hunters have something that sets them apart from normal human beings. It is not simply fighting ability. It is the ability to absorb blood echoes, and so increase their power through the use of other beings' lifeblood. In a world where so many desire to become powerful enough that they may be the surrogate for a Great One's child, the implication is obvious.