The Playing Card Soldiers are characters from Alice's Adventure's in Wonderland by Lewis Carroll. They are controlled by The Queen of Hearts. They look like playing cards with heads, arms and legs.
For more on Lewis Carroll's Playing Cards, go here.
Appearance and Personality
"They were each eight feet tall and four feet wide. They bore numbers and symbols of hearts, clubs, spades, and diamonds."
In Beyond the Kingdoms, The Playing Card soldiers follow the Queen of Hearts into the Land of Stories. In An Author's Odyssey, it is mentioned how they attacked the Center Kingdom and the Eastern Kingdom for the Masked Man.