The Wicked Witch of the West made her name in Oz by ruling over, and enslaving, the Winkies. When she learns that Dorothy Gale has killed her sister, the Wicked Witch of the East, she attempts to kill the child, only to be thwarted by the Good Witch of the North's protective spell.
Instead, she imprisons Dorothy and the Cowardly Lion, her underlings having dispatched the Tin Woodman and the Scarecrow. The Witch, believing the silver shoes to be hers by right, attempts to steal them from Dorothy. However, due to the nature of the shoes, she may not remove them, and must instead wait for Dorothy to remove them.
In an effort to speed this process along, she causes Dorothy to trip, whereupon one of the shoes falls off. Angered by this, Dorothy takes a nearby bucket of water and splashes it upon the Witch, which causes the Witch to disintegrate.