In Richard III who said A horse a your kingdom for horse?

The famous line is actually "A horse! A horse! My kingdom for a horse!" and it's spoken by Richard III himself in Act V, Scene IV of the play.

This occurs during the Battle of Bosworth Field, where Richard is fighting against Henry Tudor for the throne. He has been separated from his troops and is surrounded by enemy soldiers. He cries out for a horse, desperate to escape the situation, even offering his kingdom in exchange.