However, the witches mention in Wyrd Sisters that the late king Verence I used to hunt people through the forest as a means of executing criminals. Such fugitives probably gave Herne his first injection of belief, sufficient to let him manifest and influence the world for however long these hunted criminals could evade their pursuers. Once he achieved consciousness, Herne hastily spread knowledge of his existence to lots of people around Lancre, so that the prayers of poachers avoiding the gamekeepers, kids playing tag, and the widespread human belief that prey-animals deserve such a deity to call upon would keep him around, albeit as an extremely frail micro-god, scarcely any more potent than Om-as-tortoise.
In the process of establishing himself in this way, Herne may also have absorbed traces of a much earlier prey-protector god: one who'd been worshiped in ancient times before the Dancers were erected, when Lancre was plagued by elves and all humans feared they'd be hunted down by them. Hence, the recently-made godling Herne freaked out when that much, much older part of him sensed that "they" were coming back.