Short answers, pulled from the story.
Eléonore Denuelle de La Plaigne (1787-1868) was the mistress of Emperor Napoleon I of France and the mother of his illegitimate son Count Léon. Her son's birth proved Napoleon could father an heir, which led Napoleon to divorce Joséphine de Beauharnais and marry Marie Louise of Austria.
Caroline Bonaparte, Napoleon's sister, arranged for Eléonore to become the Emperor's mistress.
Her son with Napoleon was named Count Léon, born on the 13th of December. He was Napoleon's first child and is recognized as proof that the Emperor was capable of producing an heir.
Eléonore married three times. Her first husband, Jean-François Revel-Honoré, was imprisoned for fraud and the couple divorced on the 29th of April 1806. Her second husband, Pierre-Philippe Augier de La Sauzaye, was listed missing in action on the 28th of November 1812 during Napoleon's Russian Campaign. She married her third husband, Count Charles-Emile-Auguste-Louis de Luxbourg, in 1814 and remained with him for 35 years until his death.
Count Léon's birth demonstrated that Napoleon could father a child, pointing to his wife Joséphine de Beauharnais as the cause of the couple's failure to produce an heir. Napoleon subsequently divorced Joséphine and married Marie Louise of Austria to secure a dynastic succession.
Eléonore Denuelle de La Plaigne died on the 30th of January 1868 at the age of 80, having been born on the 13th of September 1787.