Each of them has a "true form", who appears when Kinomoto Sakura calls the cards to use their magical powers. Most true forms are personifications; they are girls with colorful themed costumes. Except some, who are animals or creatures instead, such as The Fly (a bird), The Thunder (a giant dog), etc.
The Clow Cards were created by the Clow Reed, in their backstory. At some point in the story, the cards change appearance to become pink-ish Sakura Cards.
