What chess piece did Ron Weasley fall into to give Harry Potter the checkmate?

Ron Weasley didn't actually give Harry Potter checkmate in a chess game. He played a very important role in a chess game, but not as the one making the final move.

In the first book, *Harry Potter and the Sorcerer's Stone*, Ron sacrifices himself by falling into the Knight during a giant chess game. This allows Harry to move forward and eventually defeat the game, which is guarded by a troll and necessary to reach the Sorcerer's Stone.