These questions are never addressed in the Famous Forty Oz books. Instead, Baum introduces him as the primary villain of Ozma of Oz.
The Scarecrow briefly mentions that the Nome King is called "King Roquat of the Rocks," and Ozma explains a little about him:
"He is said to be the Ruler of the Underground World, and commands the rocks and all that the rocks contain. Under his rule are many thousands of the Nomes, who are queerly shaped but powerful sprites that labor at the furnaces and forges of their king, making gold and silver and other metals which they conceal in the crevices of the rocks, so that those living upon the earth's surface can only find them with great difficulty. Also they make diamonds and rubies and emeralds, which they hide in the ground; so that the kingdom of the Nomes is wonderfully rich, and all we have of precious stones and silver and gold is what we take from the earth and rocks where the Nome King has hidden them."Ozma is setting out to reclaim the Royal Family of Ev from Roquat and restore them to their kingdom. Although she recognizes the validity of King Evoldo giving him family to Roquat for a wasted long life, she decides that it would be best if they were restored.
However, the Nome King proved to be unlike what she expected. In fact, Dorothy right away declares that he looks just like Santa Claus, only he isn't the right color.
This important monarch of the Underground World was a little fat man clothed in gray-brown garments that were the exact color of the rock throne in which he was seated. His bushy hair and flowing beard were also colored like the rocks, and so was his face. He wore no crown of any sort, and his only ornament was a broad, jewel-studded belt that encircled his fat little body. As for his features, they seemed kindly and good humored, and his eyes were turned merrily upon his visitors as Ozma and Dorothy stood before him with their followers ranged in close order behind them.Roquat seems amiable enough but he refuses to just hand over the Royal Family, and when he reveals his massive army to Ozma, his sense of cunning comes into the forefront when he offers to let Ozma and her company try a guessing game. Each person may enter his ornament rooms to guess which ornament is an enchanted person. If all their guesses (one per enchanted person) prove wrong, they will be turned into an ornament. Ozma agreed, but soon realized that the Nome King had scores of ornaments. Ozma, her army, the Tin Woodman, the Scarecrow and Tik-Tok all failed to guess correctly. Only by sheer luck did Dorothy manage to save a prince of Ev and herself.
Roquat was furious at this turn of events and set his army to attack Ozma and her company, but due to some bumbling by Omby Amby and the Scarecrow using some of Billina's eggs, the Nomes had to withdraw, allowing Dorothy to capture the Nome King's magic belt that he used to do magic with. After using the belt to leave the Nome Kingdom, Dorothy gave the belt to Ozma.
Now deprived of his magic (and Dorothy also stopped his mechanical giant with a hammer), Roquat remained in his kingdom, the bitterness of his defeat poisoning his mind. And soon, he began to desire revenge.
Although Ozma told Roquat his name before sending him back to his kingdom, he forgot it and took the named Ruggedo. (This was no error to Baum, as there is actually a footnote in Tik-Tok of Oz explaining why he needed a new name. However, it may be a Reilly & Britton editor instead of Baum writing it.)
It turned out that Ozma had possibly made a mistake by sending the Nome King back home right away. Although Ruggedo's mind had been wiped, his Nomes apparently reminded him of his bad ways, and he became even worse than before, becoming more brutal and short-tempered. The first from Oz to witness this was Tik-Tok, who went to Ruggedo for new parts and was broken into pieces by the King's scepter. Luckily, Kaliko rebuilt Tik-Tok and he was soon sent home with gifts for Ozma.
Maybe it was long-lasting effects of the Water of Oblivion, but Ruggedo did not seem to learn from his mistakes. When he found Tik-Tok later in the Land of Ev, sent to assist the Shaggy Man, he threw the Clockwork Man down a well. Finding that Tik-Tok and the Shaggy Man had joined with Queen Ann and her army of conquest, he played a number of tricks on them, assisted by his magician, the Long-Eared Hearer, and Kaliko at the Magic Spyglass, who warned Ruggedo to take care. Kaliko's words were ignored and Ruggedo made the biggest mistake of his career as King of the Nomes: throwing the entire invading company down the Hollow Tube to the great fairyland where Tititi-Hoochoo reigned.
Tititi-Hoochoo, the great Jinjin, had warned Ruggedo not to use the Hollow Tube, and now that he had been defied, it was time for Ruggedo's punishment: the victims of the Tube would be sent to the Nome Kingdom by riding a dragon named Quox, him serving as an instrument of vengeance. Fighting the Nome army and even defeating some transformations by Ruggedo, eventually, Ruggedo was stripped of what magic power and knowledge he had just by looking at Quox's ribbon and scared off by some eggs. Ruggedo was no longer the Nome King, and Kaliko (who had proved friendly to Betsy Bobbin) was made his successor. Kaliko, however, offered Ruggedo refuge in the Nome Kingdom. (After he miserably failed in carrying off gems from the Metal Forest and assisted in disenchanting the Shaggy Man's brother, who he'd captured and enchanted before.)
However, when Baum next featured Ruggedo in The Magic of Oz, he was now exiled from the Nome Kingdom, though he told Kiki Aru that he abdicated. Apparently, he had stirred up some sort of trouble in the Nome Kingdom, making Kaliko give him the boot!
Ruggedo told Kiki many things that weren't quite true. His bitterness at being ousted from his throne and home likely led to self-justification, and he wanted to win Kiki to his side, so he painted himself up to be a "good guy." Learning that Kiki Aru could transform himself and anything he wished, Ruggedo came up with a plan to conquer Oz by going to the Forest of Gugu disguised as fantastic beasts called Li-Mon-Eags, convince the animals that Ozma planned to attack them, and start a revolt against her. The plan nearly worked until the meeting with the animals was interrupted by the arrival of the Wizard and Dorothy. Kiki panicked and transformed almost everyone present into another form, including Ruggedo, who became a goose. Later, the Wizard learned Kiki's magic word and turned Ruggedo and Kiki into nuts.
At the close of The Magic of Oz, Ruggedo and Kiki are restored to their true forms and made to drink of the Water of Oblivion. Ruggedo is allowed to stay in Oz as a wanderer. And that is the last Baum wrote of him.
Later, in The Gnome King of Oz (Thompson, unlike Baum, insisted on spelling "nome" with its traditional "g"), he met Peter Brown and with the boy's help, left the island behind and attempted to conquer Oz again with an invisible cloak. He came very nearly close to capturing Ozma, until Peter silenced him with the Silence Stone. Again, he was dunked in the Water of Oblivion.
In Pirates in Oz, he has managed to leave Oz and become King of the coastline Kingdom of Menankypoo, where the effects of the Silence Stone are removed, and he allies with a mechanical man named Clocker and fierce pirates to take over Oz, which Peter and Pigasus manage to stop at the eleventh hour. Ruggedo is turned into a stone jug.
In Handy Mandy in Oz, the Wizard Wutz breaks Ruggedo's enchantment to help him take over the Emerald City again, but Himself the Elf manages to turn the two into cacti, and this is the last time Ruggedo appeared in the Famous Forty Oz books.
Ruggedo has appeared in many Oz books outside of the Famous Forty, often getting up to some trouble, and usually winds up being mind-wiped, exiled, imprisoned, transformed, killed, destroyed, and occasionally, he reforms.
When I set out to write Outsiders from Oz, I initially didn't intend to include Ruggedo. He wasn't part of the original plan to have the Wizard and Button-Bright visit the valley of Mo, and he wasn't part of the original Ozma plot. But when the Ozma plot went underground, it was almost impossible not to reference the Nomes. Reading Peter Blystone's translation of Alexander Volkov's The Yellow Fog, I decided that I did want to handle the character of Ruggedo, and I wanted to do it in my first Oz book.
In The Yellow Fog, we find Urfin Jus, who had previously been exposed to the Soporific Waters, which temporarily wipe a person's mind, allowing them to learn good habits in the interim. Urfin is treated kindly by the people of the Magic Land and as a result, when he finds temptations to do evil, he refuses. Not only this, but when the Yellow Fog descends, he helps find ways to keep everyone safe from it. A number of Oz fans believe that Urfin owes some of his origins to the Nome King, so getting a bit of inspiration from this book, I went on to add Ruggedo to Ozma's underground experience in my book.
I decided to mainly pick up where Baum had left Ruggedo, though Outsiders does acknowledge Thompson's addition to Oz. When I mentioned this to Eric Gjovaag at the Winkie Convention in 2011, he agreed with my editor and I that given Ruggedo's many, many experiences in the Famous Forty and other books, just having him pop up without his full memory and no explanation as to why he isn't a cactus anymore was actually a better idea than trying to explain it. In this case, it was better to just tell the story than to worry about what is admittedly a rather messy and foggy continuity. Joe Bongiorno's Royal Timeline places Outsiders from Oz between The Magic of Oz and Kabumpo in Oz. It was my intention that it actually takes place long after the Famous Forty Oz books, but if a reader wants to see it differently, they are free to.
I won't spoil Ruggedo's story in Outsiders, but I knew I wanted to do something different with him than have him get angry and try to take over Oz once again. A conscious choice was to call him "Ruggedo" rather than "The Nome King" (as Thompson often did, spelling it "Gnome") since he wasn't the Nome King anymore, though his past as king was actually a plot point.
I do believe I will be using Ruggedo again in a future Oz tale, but it's no wonder why people like Ruggedo. He is a wonderful Oz villain not because he can be so mean, but because anyone could be like him after a bad day. His gripes are sometimes quite relatable! But whether he's grumpy, imprisoned, mind-wiped or actually happy, he's a wonderful character, and let's face it, Oz wouldn't be the same without him.