When we learn that the Hunter will fight the Rider in the woods, we're not sure what to make of it since we don't know the guy very well—or at all, really. Before the Hunter and the Rider can duke it out, Will hands over the carnival mask his brother gave him to help the Hunter defeat the Dark. It's kind of an ominous moment:
The dark branches of Herne's antlers curved up over Will, the moonlight glinting on their velvety sheen, and the Hunter laughed softly. He looked down at Will out of his yellow eyes, in the face that was no longer a mask but living, and he spoke in a voice like a tenor bell. "The Signs, Old One," he said. "Show me the Signs." (12.31)
The guy's a little creepy, right? Especially with "yellow eyes" and a big horned mask on his head. Luckily, the Hunter's all he's cracked up to be and he plays his part in getting rid of the Rider and the Dark. So in the end, while we know virtually nothing about him, we do know something super important: He's on Will's team. Phew.