My horse Introduction
I'm Richard III. I really want the crown and I'm willing to do just about anything to get it. Lie, manipulate, murder, you name it. As long as the precious crown is on my head, I don't care what I do. And you know what I think?
Slave, I have set my life upon a cast,
And I will stand the hazard of the die:
I think there be six Richmonds in the field;
Five have I slain to-day instead of him.
A horse! a horse! my kingdom for a horse! (5.4.9-13)
Who Said It and Where
Richard is Duke of Gloucester, and, man, is he unhappy about it. In the beginning of the play, he tells us that his brother Edward has become the king of England after a series of long civil wars (a.k.a. the Wars of the Roses) between his people (the Yorks) and the Lancasters.
Despite the happy news about King Edward and his family's victory, Richard is bummed and feels inadequate because (1) he was born a "deformed" hunchback and (2) he's got no love life to speak of. Richard lets the audience in on a big secret: to amuse himself, he's hatched an evil-genius plot to get his hands on the crown. Because why not?
After killing a bunch of his family members and spreading mean rumors about the ones he let live, Richard successfully snags the crown, plops it on his head, and acts like he's doing England a really big favor.
But Richard's still not happy. Go figure.
Meanwhile, the Earl of Richmond (a.k.a. Richmond) is gathering troops and allies in France so he can storm England and take Richard down. Also, the everyday Joes of England have caught on to Richard's shenanigans and have just about had it with the guy. Even Richard's mom has turned against her son and cursed him to die in battle.
In this scene, Richard seems to have taken to the battlefield in crazy-desperate mode. His horse has been killed, and he is wandering the battlefield on foot, killing everything in his path with a fatalistic fury.
Richard yells out the famous line, "A horse, a horse! My kingdom for a horse!" He is mad with bloodlust. He says he's slain five of the six "Richmonds" on the field, but not the Richmond he wants. (It was common practice to dress a few guys up as the leader of the troops to serve as decoys. Swell job, huh?) Richard runs off again, looking for horses and the real Richmond.