Jacks were originally known as “Knaves.” Because King and Knave both started with the letter “K”, the slang term “Jack” was commonly used and eventually Knave was phased out. In France, the card was called the ‘Valet’.

Jacks are sons of the Kings. ... It is believed that Jack of Hearts wins his crown through sacrifice for love.

Étienne de Vignolles, called La Hire, was a French military commander during the Hundred
Years’ War, and a close consort of Joan of Arc. La Hire was one of few military leaders who believed in Joan, fighting along her at the battle of Orleans.

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