The cast of War Horse— Robert Emms, Jeremy Irvine, Patrick Kennedy, Benedict Cumberbatch, and Tom Hiddleston—flanked by Lusitanos Rico and Fuego, photographed at Tilsey Farm, in Bramley, near Guildford, Surrey, England.

Some of the greatest stories of all time have been narrated not by a human but by a horse. Black Beauty, the first-person bildungsroman of an English colt, is said to be the sixth-best-selling book in the English language. Leo Tolstoy’s Strider and Rudyard Kipling’s The Maltese Cat both have narrators who nicker and snort. More recently, Joey—the stoic, “red bay” voice of Michael Morpurgo’s War Horse, of 1982—has joined the pantheon of maned-and-tailed storytellers with a moral message. Joey is witness to World War I, the last major war to employ cavalry and cart.

In 2007, Joey’s story found a whole new audience when the Royal National Theatre of Great Britain turned War Horse into a theatrical tour de force, complete with life-size horse puppets. (The production is currently running at Lincoln Center Theater, in New York, and just won a slew of Tony Awards, including for best play.) This December, Joey leaps to the big screen in a movie directed by none other than Steven Spielberg. “I heard about it from several people,” Spielberg says. “My wife and I flew to London, and we attended a weekend performance of War Horse, and that’s pretty much what sealed the deal. I had never been that interested in World War I, but this story of the last war that used the horse and abused the horse was so strong I thought it would translate wonderfully into a film with real horses.”

Joey doesn’t narrate anymore—“Every medium has its point of view,” explains Spielberg—but he remains the point of connection between doomed young men from both sides of the fighting. Albert Narracott, the farm boy who loves and raises Joey—and who enters the war to find Joey—was key to the casting. “Hundreds of young boys came in to read for the part of Albert,” says Spielberg. “And then one day Jeremy Irvine came in and did a cold reading. Not only was he a great-looking 18-year-old, but his performance was very natural, very authentic.” Previous to this, his first film, Irvine had been working in the chorus of the Royal Shakespeare Company, playing a tree. “Quite literally,” Irvine says. “I’d come offstage with two branches.”

Joey, as is usual in moviemaking, will be played by more than one horse. But does he still have four white stockings and a white cross on his forehead? “Of course he does,” Spielberg answers. “To cut that out would have been to cut out the heart of the story.”

Read more: Vanity Fair