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Cut and pasted from Wikipedia:
"The Wicked Witch of the West is a character and the main antagonist in the fictional land Oz created by American author L. Frank Baum in his children's book The Wonderful Wizard of Oz.
In the 1939 feature film "The Wizard of Oz", Margaret Hamilton plays the Wicked Witch of the West as a stooped, green-skinned witch, dressed in a long black dress with a black pointed hat. This representation of the Wicked Witch has become a standard for what witches look like and an archetype for human wickedness.
While this relationship is not mentioned in Baum's books, in the movie, the Witch is the "sister" of the Wicked Witch of the East, who is killed when Dorothy Gale arrives in Oz. As a result, the Wicked Witch of the West's role is made more prominent as she seeks revenge against Dorothy for killing her sister."
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