A king isn’t exactly the most typical piece to threaten the other king with a checkmate, yet it’s still capable of dealing the death blow. Of course, the only possible way is to do it indirectly as a discovered check. See the example:
So yes, the checkmate was really delivered by the king move exposing the bishop. Neat, huh? It’s unlikely that such a game would be played unless both players agreed on doing some kind of exhibition to demonstrate the hidden potential of chess rules. But did a king’s checkmate ever happen in a serious game between masters?
The answer is yes and no. The famous game between Edward Lasker and George Alan Thomas in London 1912 is usually mentioned as the best example. However, it’s not fully clear if the notation reflects the real situation, as many different versions of it were published in various newspapers and bulletins. Eh, whatever. The fantastic queen sacrifice and the black king march to the first rank alone make the fight worthwhile, and Lasker’s brilliancy is one of the most celebrated games in chess literature. Just observe and admire the final combination:
Allegedly, Edward Lasker commented on his outstanding victory later:
Instead of checkmating with K-Q2 I could have done it by castling, which would perhaps have been more spectacular, as no player has ever been mated that way before, as far as I know. I actually considered castling, but the efficiency-minded engineer in me got the better of it and I played K-Q2 which required moving only one piece.
Note the unusual shortcode K-Q2 instead of the usual Kd2. It was pretty common in 1912 to use the descriptive notation, especially in English, French, and Spanish chess literature. Since 1981, FIDE no longer recognizes it for the purposes of dispute resolution, and algebraic notation is now the accepted international standard.
So, that was something that had happened 111 years ago! (that’s a nice number) What about the present time? The king’s checkmate problem piqued my curiosity, so I modified the BrainKing.com database search script, and executed it with a command that would be equivalent with “find all chess games that ended with a checkmate delivered by a king”. To my surprise, 29 results have been found! Despite the low chess quality of the most of them, at least one game might be worth publishing. It contains some bad blunders, but the final 2-move combination just looks nice: