House of the Dragon

 

House of the Dragon explores the beginnings of the bloody civil war that broke out between the Targaryen family during their reign over Westeros. Known as the Dance of the Dragons, the war almost annihilated the dragon-wielding house.

In short, it is not necessary to have seen Game of Thrones to watch House of the Dragon because it is a prequel. None of the events of Game of Thrones directly affect the spin-off; it is the other way around. The fall of the Targaryen dynasty and the family's civil war has an impact on the last Targaryen, Daenerys (Emilia Clarke), in the original show.

In that sense, it is not important to have watched Game of Thrones in order to understand House of the Dragon. 

here are many more Targaryens and Targaryen-adjacent people to keep track of, but let's pace ourselves.

Another good thing to remember is that many people in Westeros believe the Targaryens have a genetic tendency towards insanity. (Ser Barristan Selmy put it best: "Every time a new Targaryen is born, the gods toss a coin in the air and the world holds its breath.) So even the good ones are, theoretically, one minor inconvenience away from mass murder.

 Steve Toussaint as Lord Corlys Velaryon, Eve Best as Princess Rhaenys Targaryen.