Will White Walkers appear in House of the Dragon?
Ah, the White Walkers. They were the biggest threat to everyone and everything in the Game of Thrones.
Certainly, human villains were sly and pernicious, and their antagonistic relationships with the heroes were more personal, but the White Walkers and their Night King were an unmatched destructive force.
These inhuman creatures of cold and death from beyond the Wall had both the intent and the ability to unleash apocalypse on the continent of Westeros and probably beyond, by annihilating humanity with their armies of walking dead and casting the world into eternal winter.
And they are ancient creatures, literally predating written human history, with the Night King being several thousands of years old. As House of the Dragon is a prequel to Game of Thrones, they and their wight minions are definitely around at the time when Rhaenyra Targaryen and Aegon II Targaryen are fighting over the Iron Throne – albeit sealed beyond the Wall and relatively inactive.
Could the White Walkers appear in House of the Dragon, then?
Well, the short answer is "no". And the long answer is "most likely no, save perhaps for a few more hints and teasers of their existence."
None of the several versions of George Martin 's story, on which House of the Dragon is based, features the White Walkers in any capacity. Furthermore, they, frankly, have little conceivable place in a story of Targaryen family drama and resulting civil war.
Now, the show is not afraid to deviate from the books. Even its framing is different, presenting one true story, instead of several accounts each of which is unreliable in its own way. And a clear reference to the White Walkers made its way into the script already – that is the prophecy of Aegon the Conqueror, of course.
But any direct appearance of the White Walkers in the show is still extremely doubtful, for the above-mentioned thematic reasons. Maybe they will get some sort of cameo in the finale. Some sort of a post-credit scene, showing that the threat, which played such an important part in motivations of King Viserys and Rhaenyra is very much real. Anything beyond that is doubtful to say the least.