Within the wider King in Yellow mythos there are many references to fictional and real people, places and concepts that the party discovered in their investigations into Alexander Roby and The King in Yellow.

• Alar is one of three cities in the land of Hastur (though this name wasn't mentioned in the play as performed) along with Yhtill and Carcosa. Alar sits on the shores of lake Dehme. The Stranger comes from Alar where he is known as Haita (Alaran for “Stranger”).
• Alar invented 'The Pallid Mask' as a foil against The King in Yellow, but it appeared to be ineffective. The wearer of the 'Pallid Mask' is the 'Phantom of Truth', who is also known as The Stranger.
• Alar is associated with Aldebaran.
• At the end of Carcosa, or The Queen and the Stranger, Alar is about to be destroyed after Yhtill and Carcosa are merged by The King in Yellow.

• Aldones is the name of the first King of Yhtill. It seems that kings in Yhtill also take this name when they become its ruler.
• On the night Aldones announced his dynasty over Yhtill he 'found The Yellow Sign'. What this means is unknown, but it seems to be a sore topic in Yhtill.
• Umberto uses the name Aldones when dealing with Julian Knight in order to catch the interest of, and thereby verify the identities of, the other investigators on board the Viceroy of India.

• Camilla is the daughter of Cassilda, Queen of Yhtill as described by the play Carcosa, or The Queen and the Stranger.
• Camilla's main role is to determine of the succession of the rulership of Yhtill by choosing which of her brothers to take as her husband. She refuses to accept the diadem of rulership herself as she is fearful of receiving The Yellow Sign.
• In Carcosa, or The Queen and the Stranger, Camilla is played by Jean Hewart.

• Cassilda is the queen of Yhtill. She has two sons (Thale and Uoht) and one daughter (Camilla). She bears the Diadem, which appears to be the symbol of leadership in Yhtill.
• Cassilda would like to give the diadem to Camilla, but she refuses because she fears seeing The Yellow Sign which is the fate of rulers of Yhtill. The two brothers both want the diadem, and it seems that who gets it depends on which of them Camilla chooses as her husband (Yhtill evidently has some odd views on incest).
• Cassilda appears to have the power to change things in Yhtill which is stagnant, but chooses not to.
• In Carcosa, or The Queen and the Stranger, Cassilda is played by Hannah Keith.

• The name of the title character in Ambrose Bierce's 'Haita the Shepherd', Haita is also used in Talbot Estus' play Carcosa, or The Queen and the Stranger as the real name of The Stranger, although it is stated that the word simply means 'stranger' in the language of [#[Alar]].

• Common to all versions of the story of The King in Yellow, Hali is the name of the lake on which the city of Carcosa sits.
• It is also used as the name of a prophet in the stories of Ambrose Bierce.

• The significance of this is unknown, but the Hyades is a open star-cluster located in the constellation Taurus.
• The brightest star in the Hyades is Aldebaran. The Stranger in the play Carcosa, or The Queen and the Stranger claimed Aldebaran as his star.

• Thale is the elder son of Cassilda in the play Carcosa, or The Queen and the Stranger. He is played by Walter Paige.

• The Pallid Mask is alluded to, but never described by Robert W Chambers in his stories of The King in Yellow.
• In the play Carcosa, or The Queen and the Stranger, The Stranger wears a featureless white mask of which he tells the people of Yhtill to wear copies to protect themselves from The King in Yellow. At the end of the play, the Stranger, now called Haita reveals that that which appears to be a mask is in fact his true face.
• When the King makes his appearance at the end of the play, and overwhelms Haita, he curses the people of Yhtill and tells them that the price of victory over Alar shall be 'the fixing of the mask'.

• The Stranger is the driving force behind the plot in the play Carcosa, or The Queen and the Stranger. His arrival shocks Cassilda and the people of Yhtill out of their stasis. Unfortunately, his defiance of The King in Yellow lands him and the people of Yhtill in big trouble.
• The stranger is always seen wearing a mask, but in the end insists that he is 'The Pallid Mask' and 'The Phantom of Truth'. He wears The Yellow Sign as a mark of defiance of The King in Yellow. According to the script of the play, the stranger's name is Haita, and he hails from Alar.
• The stranger claimed Aldebaran as his star.

Yhtill is one of three cities in the land of Hastur (though this name wasn't mentioned in the play as performed), along with Alar and Carcosa. Yhtill sits on the lake of Hali. It has a hereditary monarchy descended from its first king Aldones (Yhtillic for 'father'). The current ruler of Yhtill at the time of the play Carcosa, or The Queen and the Stranger is queen Cassilda.

• Yhtill is at war with Alar and has been for a long time. The City has become stagnant, almost detached from time.
• Yhtill appears to have some odd views on incest as the succession of the rulership of the city (symbolized by the possession of a diadem) is decided by the queen's daughter choosing one or her brothers to marry.
• The rulers of Yhtill fear receiving The Yellow Sign.
• The city (and its rulers) are associated with the Hyades.
• At the end of Carcosa, or The Queen and the Stranger, The King in Yellow merges Yhtill with Carcosa to destroy Alar.