Extinction chess

Extinction chess is a chess variant invented by R. Wayne Schmittberger, editor of Games magazine, in 1985. Instead of checkmate as the winning condition, the object of the game is the elimination of all of a particular kind of piece of the opponent. In other words, the objective is any of the following:

Since the king is not a special piece in this game, it is legal to castle when in check, or to castle through check. The other rules of castling are the same: the king and the rook have not moved, and there are no pieces in between. Promotion to king is also allowed. (Although losing the king loses the game, it can legally be captured. If there are two kings of the same color, e.g. after a promotion to king, either may be captured without the loss of the game.)

Bibliography

...
Wikipedia