Mrs. Lantin was loved deeply by her husband, and although she was a dutiful wife, she was also dishonest, selfish, and disloyal. While he worked hard all day and came home each night, she insisted on going out to the theater and going to social functions. She would spend hours in the evening admiring her beautiful jewels. It was not until after her untimely death that Mr. Lantin discovered that the jewels he believed to be fake were real and worth a great deal of money. The only way she could have obtained these jewels was through receiving them as gifts from other men or purchasing them herself with money from other men. It ws this realization that caused him to collapse in the street and go home and cry all night. This makes her an antagonist to the protagonist Mr. Lantin. Her selfishness actually contributed to her death and his misery.
This short story by Guy de Maupassant is also known as "The Jewelry."
There really cannot be said to be any antagonist in this story. The two principal characters are M. Lantin and his wife. The husband, of course, has always been taken for the "injured party" simply because of the shock of realization when he discovers the truth about his wife.
However, this does not automatically make the wife the antagonist. After all, consider these factors: The Lantins could live in ease because of the added (and unknown) income of the wife. During their life together, M. Lantin is probably the happiest husband one could think of. After the death of the wife, she still adds to Lantin's happiness by enabling him to become a rich man, leave his job, take a second wife.
If the reader insists on having an antagonist to the story, one may be found at the closing lines of the story. The second wife: She made M. Lantin miserable.
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