Who are the white walkers in Game of Thrones?

Related questions

1. Who is going to die Game of Thrones?
2. Why was Jon Snow a traitor?
3. Is Sansa Stark a virgin?
4. Did Brandon Stark die?
5. Did Khal Drogo die?
6. Can Bran Warg into a dragon?
7. Can bran stark change the past?
8. Is Arya Stark blind forever?
9. Does everyone die in Game of Thrones?
10. Is Hodor a stark?

Tags

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2. #thrones
3. #referred
4. #humanoid
5. #dwell
6. #threat
7. #novel
8. #creature
9. #walkers
10. #television
11. #martin
12. #george
13. #westeros
14. #north
15. #white
16. #which
17. #walker
18. #others
19. #primarily
20. #mankind
21. #supernatural
22. #based
23. #novels