To know the story of Ozma, you must first understand that there was never only one of her. Ozma is a name that has been passed down mother to daughter since Ozma the First (sometimes called Ozma Initiata).
Long, long ago, Oz was ruled by a very old, kind, and gentle human king with mortal blood named Pastoria. It is rumored that Pastoria was also once deeply in love with a beautiful enchantress named Lurline, the Fairy Queen of great magical power. It was she who first chose the land to make her country. She herself used her magic to create its breathtaking landscapes, its sparkling rivers, its rocky mountains with high waterfalls, its pine filled forests and thick marshes, its vast hills and colorful flowery meadows. And after it was finished, Lurline cut the land off from the rest of the world and named it Oz. She and Pastoria, along with the people of the fairy Kingdom lived among these lovely sights for a long time in harmony and bliss.
Lurline and Pastoria eventually had a beautiful baby girl that Lurline named 'Ozma,' the first fairy child of Oz. As she was half human and half fairy, she was immortal like Lurline even though Pastoria was not. After that Lurline left the land of Oz, putting Pastoria on her Throne and leaving Ozma in his care before disappearing forever.
King Pastoria lived a long and wise life. But he became very, very old - with wrinkled skin and a long white beard. Now widowed and left with his baby infant, without the guidance of Lurline, Pastoria was not a very powerful King and was only getting older. He lived in a rather small Kingdom, in the middle of the land. His people were happy and content as his subjects, but there was trouble for them.
The land of Oz was also ruled by two Bad Witches - one of the East and one of the West. They had enslaved many in Oz - the Witch of the West had enslaved the Winkies and Winged Monkeys, and the Witch of the East her magic to keep the Munchkin people tightly in her bondage.
The two Witches tried many, many times to overthrow Pastoria and take over all of Oz. Unfortunately Pastoria himself did not know the magical arts. He had always depended on Queen Lurline's magic. Alone, he could not defend himself or his people. The East and West Witches could have easily taken over and stolen the King's Throne, but one thing stood in their way - the two Good Witches Locasta Tattypoo, of the North and guardian of Gillikin Country, and Glinda the First, who ruled the southern Quadling Country.
The two Good Witches used all the power and sorcery they knew to protect poor Pastoria and his people from harms way. But they were not strong enough to banish the Wicked Witches out of Oz or put an end to them and the Wickedness that dwelled within the land of Oz all together.
When Princess Ozma took her rightful place back as the official heir to the Royal Throne to rule over Oz, with the help of Glinda, she created The Great Spell, halting the aging process in Oz forever and eliminating any unpleasant diseases or fatal deaths in general. Deaths in the land of Oz could henceforth only happen through disastrous accidents or very powerful magic, and no one was forced to age a single day and get older in appearance if they did not wish to. Also with the help of the First Glinda, she sealed Oz off from the rest of the world entirely. Or so she thought.
After these spells, much of the concrete history of Oz was lost. All that remains are the mythologies of the first Ozma and the first Witches of the North, South, East, and West. There is no clear history of what happened to them. They faded into myth, into obscurity, into the collective understanding of the land and the beliefs of the people. Lines of Ozma passed, kingdoms rose and fell and progressed. And, in time, records arose again.
After few hundred years and many generations of Ozmas, a man came out of the clear blue sky. He was aloft in a large air-craft of sorts which slowly descended from the clouds up above. When he finally reached the ground, Ozians were astonished by this unexpected arrival. They had never seen such a peculiar invention or such a peculiar traveller. From inside the basket of the giant balloon, he addressed the crowd and called himself "Oscar Diggs", enthusiastically introduced himself as a great Wizard and gifted Magician. The people of Oz believed him as they saw him perform magic tricks right before their very eyes. The people of Oz asked if the Wizard would be the ruler of the land and he agreed that he would look after Oz and someday rid the land of it's ailments and wickedness if they promised to obey his every wish and demand. The people of Oz believed him and agreed. It was the Wizard who proposed the building of the famous Emerald City in his own honor and constructing the Yellow Brick Road that lead to the main entrances from every country in Oz.
Ozma Tippetarius at the time was an infant, but her blood was still magical. The people knew that she was destined to rule, just as all Ozmas before. But many people were upset about this. Many Ozians were tired of being ruled by only Ozmas, whose bloodline was no guarantee of proper leadership. Late night, someone broke into the Palace of Pastoria and snatched the baby Princess up and disappeared into the dark night. No one knows who it was - many say it was a group of politically ambitious Ozians, some say it was the Quadlings angry about their forced labor on the yellow brick road. Others say it was the Wizard himself. However it happened, the baby Ozma was given to a Witch named Mombi who lived in the North lands of Oz. Mombi was not as gifted or as powerful as the ancient horrible Witches in Oz, but she was still very ugly inside and very Wicked nonetheless. Mombi kept the baby hidden away from the Palace and to was bent on never letting anyone know where Ozma was - let alone that she was still alive.
Mombi transformed the infant Ozma into a boy and called him Tip (short for Tippetarius). Ozma, in the form of Tip, was raised as a boy and had no memory of who he really was. As Tip, Ozma created Jack Pumpkinhead. However, after the Wizard left Oz, Tip's true identity was discovered. Glinda the Good forced Mombi to transform the him back into Ozma, who was then installed as Oz's ruler.
Generations later, when word came to Ozma the Bilious that the Royal Family of the neighboring Land of Ev had been imprisoned by the Nome King, she organized a rescue party and set out to liberate them, crossing the desert on a Magic Carpet. The Nome King offered them an opportunity to save the royal family of Ev, who had been turned into ornaments in his palace, but it was a trick and soon Ozma herself was transformed into a carved emerald grasshopper. She was rescued (along with everyone else) by Billina the hen and the entire party escaped back to Ev, having confiscated the Nome King's Magic Belt. The Ozians attended the coronation of King Evardo XV and then returned to the Land of Oz.
When the Nome King planned to invade Oz and destroy it as revenge, Ozma the Bilious discovered his plans. She was surprisingly nonchalant about the threat, refusing to either prepare for war or escape the country, but merely waiting for their inevitable enslavement. Instead, she utilized a non-violent way to turn back the invaders, and Oz was once again protected.
Only a few years ago, a Wicked Witch in Winkie Country began amassing troops to take over The Emerald City. Azkadellia, a powerful Dark Witch, ruled through fear and slavery, though she held many loyal subjects who prefered her strength and ambition to Ozma, a princess who merely inherited her throne. Azkadellia and her forces marched on Ozma and had great success since Ozma was not a war leader, and her army was almost exclusively made up of peacemakers.
The Scarecrow, having been put in as her advisor, took over rulership from Ozma the Peacemaker (there are many different opinions on how peacefully or forcefully this decision was made) and set his own army against Azkadellia. The Scarecrow's army, relying on intelligence, guerilla warfare, and tik-tok inventions, began to turn the war. That is when The Great Spell broke. Both sides began experiencing heavy losses and injuries that wouldn't heal. With the entire land of Oz sent into nightmare, the three leaders came together and negotiated a truce.
Opinions differ greatly over who initiated peace. The Scarecrow, Azkadellia, and Ozma the Peacemaker were intended to rule all of Oz together. Shortly after The Great Spell broke, Ozma the Peacemaker was found to be missing without a trace. There is much speculation over whether she disappeared because of the spell breaking, or if the spell broke because she disappeared.