Children of the Forest
The original inhabitants of Westeros, the Children of the Forest are a race of elf-like beings that dwell deep in forests and caves. They are very attuned to nature and worship the Old Gods of the Forest. Though they have no formal buildings or shrines, they usually centre their worship around Weirwood trees, the distinctive red-leafed trees like the one in the Godswood at Winterfell.
Generally considered extinct, as they have not been seen in 6,000 years, the Children of the Forest are masters of hiding. A recent group lived with the Three-Eyed Raven beyond the Wall, until they were destroyed by wights. It is not currently known whether they are now truly extinct.
In the "The Door" episode, it is shown that the Children of the Forest created White Walkers.