"We've got four, maybe five, plus whatever aliens might be up to, but... okay. You're getting the short version, and I've never done the short version for someone who wasn't, like, seven, so stop me if I start explaining something obvious.
"This story is true. In the time before time, when the world was whole, Mother Luna, whose light held back the entities of the Abyss, looked down on the world and saw Father Wolf, greatest of the earthbound spirits. They fell in love, and in time, uncountable as all time was then, brought their children into existence. These were the Firstborn, and they inherited Father Luna's quicksilver change and Mother Wolf's powerful form. Before that time, Father Wolf alone prevented other spirits from preying too heavily on mortals, who were then barely more than the cleverest animals among many, but her children joined in the hunt and became the first pack.
"Gradually, though, Father Wolf began to weaken. She could no longer patrol all the quiet places of the world, and powerful spirits began terrorizing and controlling entire tribes of mortals, while the Plague King and the Spinner Hag fractured themselves into shards unnumbered, far too many for him to catch at once. The Firstborn knew then that it fell to them to bring the world back into harmony, and if they were to have the power to do that, Mother Wolf had to die. It is no easy task, to kill even a small spirit, and even weakened Father Wolf was still the greatest among them. But every spirit has a bane, and Mother Wolf's was the teeth of his children, and so the five Firstborn in concert brought her down.
"And it worked, though not as they expected: in the dying, Father Wolf raised such a howl that it tore the world in two. No longer could spirits wander freely among mortals; no longer could mortals seek out spirits. Only the Firstborn and their children could navigate the Gauntlet between the worlds, and Mother Luna in his grief and rage turned her faces from us. Now it falls to us to guard the border, to keep spirits from spilling into the world of flesh and to keep mortals from starving the spirit world, and to stop the shards of the Hosts rejoining themselves, and so it will fall to our children after us."