During and after the French Revolution no images of Royalty were allowed. The guillotine was the punishment for anyone producing any royal imagery, so playing cards had to be altered to remove the links to royalty. The King was replaced with Prosperity, the Queen became Liberty and the Jack was depicted by Equality. These were derived from the motto of the revolution: Liberty, Equality and Fraternity.
The Revolution also changed the Ace and its use. It used to be the lowest card the 'one' but after the revolution it was transformed into the highest card. It is thought that the new 'aces high' way of playing the ace symbolised the lower, working classes rising high and seizing power from the royal family.
When Napoleon became the Emperor he restored the use of the King, Queen and Jack, since they were no longer seen as a threat the to Repbulic of France.