The Wicked Witch of the North, named Mombi, is a fictional character in L. Frank Baum's classic children's series of Oz Books. She is the most significant antagonist in the second Oz book The Marvelous Land of Oz (1904), and is alluded to in other works. Mombi plays a very important role in the fictional history of Oz.
The character was originally presented as a lowly hag who had enchanted Princess Ozma in order to prevent her from ascending to the throne. Later in the series, L. Frank Baum specified that she had once conquered and ruled the Gillikin Country, as the Wicked Witch of the North, only to be deposed by the Good Witch of the North.
Furthermore, Mombi had enslaved Ozma's father ( King Pastoria) and grandfather, thereby removing the Royal Family of Oz, and enabling herself and the Wicked Witches of the East, West and South to conquer and divide the land between them.
After forcing her to disenchant Princess Ozma, Glinda the Good Witch of the South made Mombi drink a powerful draught that stripped the old witch of all her magic powers.
Mombi didn't make any further appearances in L. Frank Baum's books. In Ruth Plumly Thompson's The Lost King of Oz, the witch raises havoc once again, and at the end of the book, in a rare act of Ozite capital punishment, Mombi is ruthlessly doused with water and melts away like the Wicked Witch of the West, so that nothing is left of her but her buckled shoes. L. Frank Baum never said that all witches in Oz would die upon contact with water, but Ruth Plumly Thompson and several subsequent writers such as Rachel Payes had made that conclusion.