House of the Dragon is set well over 100 years before Game of Thrones, so it isn’t possible for any of the characters from the original show to turn up on the spinoff (well, maybe Melisandre, but I wouldn’t hold your breath.) However, there is an important prop that turns up on both shows.

In the first season of Game of Thrones, someone sends an assassin to try and kill a comatose Bran Stark, arming him with a Valyrian steel dagger. The dagger becomes a point of contention as Bran’s mother Catelyn tries to work out the mystery of who hired the assassin. Much later, Arya Stark will come into possession of this dagger, using it to slit Littlefinger’s throat and eventually kill the Night King, ending his designs on the lands of the living.

This same Valyrian steel dagger shows up multiple times on House of the Dragon. King Viserys Targaryen shows it off to his daughter Rhaenyra, saying that it once belonged to Aegon the Conqueror. Later, Alicent Hightower tries to use it to stab Rhaenyra. Some time after that, she gives it to her son Aegon upon his coronation. That dagger has had quite an eventful life!

House of the Dragon showrunner explains why they included Valyrian steel dagger

Speaking about the dagger in a House of the Dragon special feature, showrunner Ryan Condal explained why they wanted to include it. “The idea was to have some kind of legacy artifact that ties the original show to the new one,” he said.

“So this idea that Aegon who imbued his secret in this Valyrian steel dagger, the dagger that ends up passing through hand after hand after hand, that’s actually the very thing that ends the war.”

Of note is that we don’t actually know where exactly the dagger came from or who made it. Did Aegon forge it himself, or did he merely “imbue his secrets” in it, whatever that means? If HBO ever makes a spinoff about Aegon the Conqueror, the first Targaryen king of Westeros, perhaps we’ll find out then.