There are usually two Jokers per deck, and the artwork on the card varies depending on the deck's publisher. Often, one Joker card will be in black and white, while the other will be in full color. The joker often shows a court jester.
The Joker's use is greatly varied, as well. Many card games omit the card from use entirely; others, such as Euchre make the card one of the most important in the game. Often, the card is merely a wild card and can be used as anything. The term "The Joker's wild" originates from this practice.