Poker: A Joker can be wild, or can be a "bug", a limited form of wild card which can be used only to complete straights and flushes. War: In some variations, beats all other cards. Pitch: A point card in some variations. Jokers usually are marked as "high" and "low", one outranking the other.
The Joker has no face value (rank or suit), but it acts as a wild card in the game, since it can take on any rank and suit that make optimal sense to wrap up the wanted combination.