Legal's mate is named after the French chess player Sire de Legal. The mate is from a famous game in which white sacrifices his queen. If black accepts the sacrifice, white quickly mates. The following is my analysis of this short and famous game.
1. e4 e5
White and black both fight for control of the centre by bringing out their king pawns.
2. Bc4 d6
White uses the Bishop's Opening. Most players prefer to bring the knight out before the bishop by playing Nf3. Black chooses to protect the king pawn with the queen pawn.
3. Nf3 Bg4
White develops the king knight and black chooses to pin it with his bishop. The knight is pinned because if white moves it, black can capture white's queen.
4. Nc3 g6
White develops the queen knight. Black makes a bad move with g6. The idea is to move the king bishop to g7 and control the diagonal but there is no time for this. Black should develop his queen knight by playing Nc6 and fighting for control of the centre.
5. Nxe5 Bxd1
White initiates a queen sacrifice. Black's decision to accept the sacrifice and take the queen is a mistake. He should play d6xe5 which will only leave him down one pawn.
6. Bxf7+ Ke7
White puts the black king in check. The black king is forced to move.
White's knight mates the black king. Amazingly, the black king has no escape. White has no queen but it does not matter. He has won the game.
This game illustrates that it is possible to win without the queen. Although she is an important piece, in certain situations she can be sacrificed for victory as in this well-known game.