Even with all my exposure to Kdramas, I was hopelessly lost and confused in Episodes 1 and 2 because there were so many characters to navigate! I kept having to pause the episode to decipher who everyone was and how they were related to each other (even despite all the helpful descriptive labels provided at the beginning for each character you meet).
So, here's a cheat sheet that might help you keep everyone straight. The following is a description of important titles and names of prominent characters in the drama and their significance and importance in the court/royal family:
***Don't worry, there are NO SPOILERS below, but if you want to figure everything out on your own, don't read any further.***
The Queen is the King's "head" wife and the concubines/consorts (the king has about 10 of them!) are his other wives with a lesser status than the Queen.
The Queen has five sons with the King (from oldest to youngest): the Crown Prince (the word "Crown" designates that he will be the next king) (the perfect son), Grand Prince Seongnam (the mysterious wild child), Grand Prince Gyeseong (gentle and kind), Grand Prince Muan (sweet and charming but obsessed with girls), and Grand Prince Ilyeong (into math and astronomy and "still just a kid").
Any other princes without "Grand" in front of their title are sons the king had with one of his concubines (aka Prince Ui Seong (actually the oldest of all the king's sons, even older than the Crown Prince, and a BAD EGG), Prince Bogeom (the most intellectually promising of the brothers after the Crown Prince), Prince Simso (good-hearted but struggles to measure up), etc.). There are more princes, but these are the only ones featured heavily.
The "Grand Heir" refers to the son of the Crown Prince (he's about 4 or 5 years old in this), who is next in the line of succession to inherit the throne. He will become Crown Prince when his father (the current Crown Prince) becomes king, and is technically 3rd in line for the throne.
The oldest son of the King and Queen is traditionally chosen as the Crown Prince, and is given preference over the concubines' sons in the line of succession (which is why Prince Ui Seong, despite being the oldest son of the king, is not the Crown Prince since he's only the son of a concubine).
The "Queen Dowager" refers to the mother of the current King, though interestingly, she was just one of the previous king's concubines... so, how did the current king rise to the throne despite being the son of a concubine?
I will let you figure out the rest. :)
I hope this was helpful!
NOTE for those who haven't seen many sageuks (aka historical Kdramas): I will add something here about costumes in case it helps:
The King always wears a bright red hanbok, with a gold circle embroidered on his chest, as well as gold circles on his shoulders. The Queen will have the gold patches on her torso and shoulders, like the king, but her hanbok will be different colors. The Crown Prince traditionally wears a dark blue hanbok with silver circles embroidered on his chest and shoulders.
If a character has a top-knot (a bun on the top of their head), then it's a guy. Sometimes it's hard to tell because the guys look so beautiful and they could pass for a girl, but this drama has no cross-dressing, so it's always going to be a guy. Guys with beards and dark red, purple or dark green hanboks with a square embroidery pattern on their chest with a square belt that portrudes out in front of their waist as well as hats that look like they have wings coming off the sides (I think they're called a samo) are going to be the princes' tutors and/or ministers to the King who hold power in court and advise the King.
Maidens (unmarried women) have their hair slicked back into a braid that rests tightly against their neck. Married women (so, the Queen and concubines) have their hair slicked back into a bun that sits at the base of their neck. Most of the time in this drama if you see a woman with her hair in a bun and a bright, gaudy hanbok of various colors with fabric that covers her hands resting at waist-level, you're looking at the Queen (her hanboks are usually darker, deeper colors and less gaudy) or one of the concubines. If she's old and stern, haha, it's the Queen Dowager.
