Alys Rivers will be a key player in 'House of the Dragon' if her story follows the plot of 'Fire and Blood.' Here's what to know.

Gayle Rankin as Alys Rivers in "House of the Dragon" season three. Ollie Upton/HBO Alys Rivers is introduced in "House of the Dragon" season two as a mysterious resident of Harrenhal. In the book, "Fire & Blood," Alys is a mysterious character who's suspected of being a witch. Here's what to know about Alys and her possible future in season three and beyond. Warning: Spoilers ahead for "House of the Dragon" season three, episode five, and for the book "Fire & Blood." Alys Rivers may not be a…