House of the dragon cast rickon stark, baelon rhaenyra targaryen and mysaria

In House of the Dragon, who is Rickon Stark?
This season, the Stark family may have a big part to play.
After King Viserys I's son Baelon, the "Heir for a Day," dies, he only shows up for a few seconds to swear his loyalty to Princess Rhaenyra Targaryen.
"I, Rickon Stark, Lord of Winterfell and Warden of the North, promise to be loyal to King Viserys and Princess Rhaenyra, whom he has named as his heir."
Fans of Game of Thrones will recognize Rickon's last name because the Starks were the show's main characters. Rickon was the youngest child of Eddard (Ned) and Catelyn Stark. He was 11 years old when he died during the Battle of the Bastards. (Ramsay Bolton shot him in the head with an arrow from far away. RIP Rickon. He didn't have many lines.)
In the first season of Game of Thrones, Ned Stark is named Hand of the King. About 200 years before that, Rickon's ancestor shows up in the book House of the Dragon. During this time, the Targaryens are in charge and sit on the Iron Throne. They have 17 dragons to their name, which is a lot. One house that swore allegiance to Stark was "Baratheon," which is the last name of King Robert, who rules the Seven Kingdoms at the beginning of Game of Thrones.

So far, Rickon Stark's appearance on the show is just for fans. Both the episode and the show will focus mostly on the Targaryen family. (However, Rickon's appearance does add to the story's main idea. Rickon's loyalty is discussed during a conversation between Viserys I and Rhaenyra. During this conversation, Viserys I tells Rhaenyra that Aegon I predicted that a force from the north would threaten the Seven Kingdoms. We all know that the White Walkers and the Night King are behind this threat. It's fitting that House Stark is shown swearing fealty at this time, since House Stark and House Targaryen will eventually work together to defeat this threat. (The Starks' past loyalty to the Targaryens may be a small sign of this future alliance.)
Rickon only shows up for a short time, but there may be more Stark action to come. House of the Dragon will probably show the Dance of the Dragons, which is a civil war that happens almost 30 years after the first episode. It happens when the question of who will rule after Viserys I comes to a head.
George R.R. Martin writes about this time period in his book Fire & Blood. This book is also the main source for House of the Dragon. Cregan Stark will have to choose a side during the Civil War. Cregan is Rickon Stark's son and another of Ned Stark's ancestors. By the time the Civil War starts, Cregan will probably be Lord of Winterfell.
Check out this Reddit user's graphic for a very helpful full family tree for House Stark.
Will House Stark support Rhaenyra Targaryen, who is Viserys I's rightful heir?
The rest of the season will probably answer this question for each house; we're in for another battle for the Iron Throne.