Quadlings - The ruler of the southern country is none other than Glinda, the Good Sorceress of the South. She's the longest reigning quadrant ruler, celebrating the hundredth anniversary of her rule in The Purple Prince of Oz. There's also a mention of a King of the Quadlings in Ozma and Road, and some have suspected that he might perform many of the day-to-day functions in ruling the area while Glinda focuses on her magical studies. Glinda is mentioned as the ruler in pretty much every other book, though, which makes me think that she's the actual Queen of the Quadlings, even though she isn't generally referred to as such. I wrote my own story telling what had happened to the old Quadling King when Glinda took over, and it was published in an Oziana from a few years ago.
Winkies - Moving to the western part of Oz, we come across another familiar character ruling in the yellow lands. This is Nick (short for "Niccolo," according to the Wizard stage play) Chopper, the Tin Woodman, a former Munchkin woodcutter whose flesh parts were gradually replaced with tin by the tinsmith Ku-Klip after he had cut them off with an axe enchanted by the Wicked Witch of the East. When he sought a replacement heart from the Wizard of Oz, he joined forces with Dorothy, the Scarecrow, and the Cowardly Lion. The Winged Monkeys, under the command of the Wicked Witch of the West, smashed the Tin Man against some rocks. After Dorothy melted the Witch, the Winkies in the castle restored Nick to his former tin glory, and immediately took a liking to him, inviting him to be their new ruler. He's ruled there ever since under the title of Emperor, which bothered Tip when he heard it, as the Winkie Country isn't that big. On the other hand, it DOES contain smaller kingdoms, so maybe the imperial title is more apt than Tip thought it was. While primarily known for his kindness, Nick is also known to be somewhat proud, as shown in the tin castle that he had built when the Witch's old castle grew too damp.
Gillikins - Tattypoo, the Good Witch of the North, took over as ruler of the north after conquering Mombi. As with the Quadling Country, there's a separate Sovereign of the Gillikins mentioned in Road, but there might actually be some indication as to who this Sovereign is. In Giant Horse, we learn of a man named King Gil of Gilkenny, who might well be the elusive Gillikin Sovereign. He is apparently satisfied with being a figurehead, however, as when Tattypoo discovers the secret of her past and abdicates her position, Ozma appoints not Gil, but Joe King and Queen Hyacinth of the community of Up Town in the Gillikin Mountains, as the new rulers of the northern land. While Joe is a jolly, likeable fellow, it's not clear why she would have chosen these two to rule the entire quadrant. Perhaps it was at least partially as a reward to Joe's horse High Boy, who helped to restore the Munchkin monarchy in the same book. Joe is known as both a Giant Horse (as in the title) and a High Horse (for those who prefer punny names), being twice the size of an ordinary equine, with an umbrella tail and legs that can extend and contract. It is unknown how high he can raise his body, but there's an Oziana story called "A Christmas Tree for Dorothy" in which the Scarecrow and Tin Woodman use High Boy to reach the stars and pluck some to use as Christmas decorations.
On left, Joe King meets Herby. On right, High Boy gives Philador and Herby a ride.
Munchkins - Perhaps the most confusing of the four as far as recent political history goes, the first mention of a King of the Munchkins is in Ozma, in which he is said to have met Ozma and her party at the edge of the desert on their way back from Ev. As Ev is shown as being across from the Winkie Country in almost every other Oz book, this is a bit suspect, however. There's a Monarch of the Munchkins mentioned in Road as well, but Patchwork Girl says that Unc Nunkie "might have been King of the Munchkins, had not his people united with all the other countries of Oz in acknowledging Ozma as their sole ruler," suggesting that the Munchkins might not even have their own ruler at this point. Early on in Giant Horse, Ruth Plumly Thompson states that "the blue Munchkin Country is governed by a King of whom nothing much has been heard for many a long year." Two paragraphs later, we're introduced to Cheeriobed, King of the Ozure Isles, and son of the former King of the Munchkins. Earlier in Cheeriobed's life, he refused Mombi's offer of marriage, instead marrying Princess Orin of Gilkenny (Gil's daughter) and having a son named Philador. Mombi got her revenge by capturing and enchanting both Orin and Cheeriobed's father, then cutting off the Ozure Isles from the mainland by placing a monster named Quiberon in Lake Orizon. During the events of Giant Horse, Orin returns to the Ozure Isles, and Prince Philador enlists the help of Ozma and the Wizard in saving his home islands. The Wizard petrifies Quiberon, but Ozma's magic cannot locate Cheeriobed's father, so the Royal Ruler of Oz makes Cheeriobed and Orin the new rulers of the quadrant. No detail is given on the former king other than that Ozma and the Wizard conclude he's been "utterly destroyed" (a matter on which they've been wrong in the past), but March Laumer's Good Witch reports that his name was Obadiah, and that Mombi turned his body into an acorn that grew into a tree, while his mind was trapped inside a magical wig.
Above: A portrait of Queen Orin
So what of Unc Nunkie? Well, Thompson has an answer for that as well, as her Ojo reveals that Unc's brother was the King of Seebania, and controlled most of the southern part of the Munchkin Country. When Ozma became ruler, he withdrew his claims to all but the forest domain of Seebania itself, and it wasn't long after this that the magician Mooj conquered this kingdom as well. Unc Nunkie went into hiding from Mooj with his great-nephew Ojo, but their family was restored to power in Seebania at the end of the events of Ojo. It's not clear why Ozma would have weakened the authority of Seebania, but it's known that Ozma likes to have people friendly to her in positions of power in Oz, so perhaps she limited centralized Munchkin power until she could find a ruler she knew would be loyal to her. Don't forget that she was already friends with the Quadling and Winkie rulers before taking the throne, and Glinda was probably highly influential in her early decisions anyway. Maybe Glinda had her own reasons not to trust the established Munchkin royalty.
Above: Dolls of Realbad, Ojo, and Unc Nunkie, as made by Karyl Carlson