Chess piece that can be promoted

PAWN

This humble piece starts on the second rank and is the only one that moves differently when capturing; it can become any other piece upon reaching the far side.

In chess, a pawn is the only piece that can be promoted to another piece (like a queen) when it reaches the opposite end of the board. The clue hints at this unique rule, pointing directly to the pawn as the answer. There’s no wordplay here—it’s a straightforward reference to a basic chess mechanic.