Young Griff could have changed everything about the final season.
Game of Thrones wraps up with its series finale in Episode 6 of Season 8. If you're a fan of George R.R. Martin's "A Song of Ice and Fire" books on which the show is based, though, you've probably noticed a huge factor missing from the war for the Iron Throne. That factor is Young Griff, a character who is a huge part of what's going on with Daenerys Targaryen and the Lannisters in the books, but who never appeared in the show. With the show ending, there's no chance we'll ever see Young Griff on screen, and that makes him a pretty big omission.
Young Griff appears in A Dance With Dragons, the fifth book in Martin's series. He's a character Tyrion meets in Essos, along with his Golden Company sellsword father, Griff. Not long after encountering them, though, Tyrion intuits that Griff and Young Griff are not who they appear to be. It turns out that Young Griff is actually Aegon Targaryen, Daenerys Targaryen's nephew the world has long believed dead. (This Aegon is not to be confused with Jon Snow, whose real name in the show is also Aegon Targaryen, for some reason).
To understand who Young Griff-slash-Aegon is, you'll need to remember some of the stuff that happened during Robert's Rebellion, but which has never been shown on screen during Game of Thrones. The rebellion saw Robert Baratheon, Ned Stark, and their allies depose the Targaryen royal family. At the time, the family consisted of the Mad King, Aerys, plus his kids, Prince Rhaegar, Viserys, and Daenerys (his wife Rhaella died giving birth to Dany). Rhaegar also had kids with his wife, Ellia Martell--Rhaenys and Aegon, who was an infant at the time.
Rhaegar fell at the Battle of the Trident. After that, the Lannisters sacked King's Landing, and Jaime Lannister killed Aerys. In order to prove his loyalty to Robert, Tywin Lannister ordered Rhaegar's children murdered, to remove the Targaryen heirs and solidify Robert's claim to the throne. Remember when Oberyn Martell fought the Mountain and yelled at him about raping and murdering his sister and her children? He was talking about Ellia, Rhaenys, and Aegon. In the books, the Mountain was said to have dashed Aegon's skull against a wall, and the scene was so horrific that the infant was unidentifiable.
Daenerys and Viserys survived the rebellion because Aerys had moved them to Dragonstone for safekeeping, but the claim with Aegon is that the Mountain didn't actually kill him, but instead murdered a different baby Varys put in his place. To protect him, Varys had Aegon sent across the Narrow Sea to Essos with Rhaegar's friend, Lord Jon Connington. The pair spent the rest of Aegon's life pretending to be the sellsword Griff and his son, also Griff.
So when Tyrion finds the Griffs in the books, it adds a major issue to Daenerys's quest for the Westerosi throne. Young Griff originally plans to head to Meereen and woo his aunt to help him retake the Iron Throne for himself, but Tyrion convinces him to go to Westeros with the Golden Company while the Lannisters are distracted by the War of the Five Kings. As Rhaegar's son, Aegon has a better claim to the throne than Daenerys, just like Jon Snow in the show. The sons of the prince are ahead of the king's other children in the line of succession.
It's basically impossible for Young Griff to pop up in the show at this point, for obvious reasons, and some of the ideas of that story have been reworked into those of other characters, like Jon Snow. But if Game of Thrones had gone on for longer, Young Griff could have added a lot of depth to Daenerys's story. His pressing a Targaryen claim to the throne in Westeros undercuts Daenerys's position, and could have even resulted in another Dance of Dragons, the famous Targaryen civil war that did major damage to the dynasty. There's also another wrinkle that would have added to the drama: the theory that Young Griff isn't Aegon Targaryen at all.
Martin's books contain some hints and symbolism that suggest that Young Griff could be an impostor to the throne and only pretending to be Aegon, and fans have a whole lot of theories about the situation. It's possible Young Griff is actually a Blackfyre, a member of an extinct Targaryen offshoot family that was largely made up of Targaryen bastards, who started rebellions of their own during the last hundred or so years before the events in the books. A Targaryen bastard also founded the Golden Company, so it's possible Young Griff could be related to the Targaryens (he has a lot of their distinctive features, like violet eyes and silver hair) without actually being Aegon--and that would wreck his claim to the Iron Throne.
It seems that Jon Snow is playing most of the role that Young Griff would have held in the show, at least for the most part. We've already seen his claim to the Iron Throne, as Rhaegar's legitimate son, throw Daenerys and her allies into disarray. We'll never know just how Young Griff's presence in Westeros would have changed the outcome of the final season of Game of Thrones; hopefully, Martin's last two books will finally find their way to readers and give a sense about how the story could have gone differently.
If you need more Game of Thrones coverage before the series finale, we've got plenty. Start by watching our the video breakdown of Episode 5, "The Bells," and read our review of the episode. You might also be interested in a rundown of all the Easter eggs and callbacks in the episode, a few new theories about how the finale episode will play out, and an analysis of how Game of Thrones has changed what the show is really all about.