Cross-posted from here.
The idea of villains wanting to conquer Oz is pretty much a cliché at this point. While it's largely apocryphal Oz stories in which this plot device is overused, there is precedent for it in the Famous Forty. Would-be conquerors include the former Nome King, Ugu the Shoemaker, Kiki Aru, Mogodore the Mighty, Skamperoo of Skampavia, Strut of the Strat, and the Mimics, as well as the Wizard of Wutz. The villain of Handy Mandy in Oz was King of the Silver Mountain in the northeastern Gillikin Country. He ruled over a well-organized but unhappy populace inhabiting a series of caverns within the mountain, many of whom worked as silver miners. Wutz invented a transportation system much like a roller coaster to access different parts of the mountain.
Wutz's own powers are largely based on quicksilver bubbles that he blows from a silver pipe, but he has other magic as well, including his stupefying powder. He also employed secret agents known as M-Men to infiltrate various areas of Oz and steal more magic for him. As the story begins, Wutz already has Glinda's Book of Records, and Agent Number Five steals Ozma's Magic Picture and the jug in which the former Nome King had been transformed at the end of Pirates. By means of a cheap plot device, Handy Mandy inadvertently breaks Ruggedo's enchantment, and he teams up with Wutz to conquer the land. Like many villains who have formed uneasy alliances, however, the two monarchs end up quarreling, giving Mandy the opportunity to save the Emerald City with the Silver Hammer. Himself the Elf turns both of the plotters into cacti, a form which Ruggedo escapes in several apocryphal stories , but I don't know of any tales that restore Wutz. I have an idea for a plot in which a group of rebellious Nomes who are trying to bring back Ruggedo accidentally disenchant Wutz instead, but I haven't gotten much farther along than that.
Ruth Plumly Thompson gives a fair amount of description for her villain. The wizard is a tall and regal man with thick silver hair and piercing violet eyes, who wears a tight-fitting purple suit with a jeweled belt and sword. His mood can switch from calmly pleasant to ragingly angry in no time at all. He's a tyrannical ruler, punishing people who disobey him by trapping them in flowerpots. He also treats his agents quite poorly, hoping that it will keep them competing with each other for his favor. It's been proposed that Neill's drawings of Wutz are based on a young John Barrymore.
After Himself turns the wizard-king into a cactus, Ozma makes some adjustments to the Silver Mountain itself. She moves the cliff dwellings of the inhabitants to the outside of the mountain, which hopefully is a welcome change, but I wouldn't be too sure. After all, their whole lifestyle is based around living inside the mountain. Besides, since when does Ozma have the power to turn a mountain inside out, Magic Belt or no Magic Belt? The ruler of Oz also appoints Wutz's long-suffering assistant Nifflepok as the new King of the Silver Mountain, even though there's no indication that he's done anything to prove himself deserving of this position. Thompson was obviously in a hurry to finish her story (something I can certainly understand) and left some loose ends.
 Ruggedo is restored from his cactus form in Raggedys, Enchanted Gnome, Grown-Up, Medicine Man, and Unknown Witches. Deadly Desert puts a bit of a twist on this by having Ruggedo become a walking cactus for a little while.