That boy is Albert Narracott, a Devon farmer’s son who raises Joey from a spirited colt to a stallion who adapts, of necessity, to farm work. With the advent of World War I, Albert’s father sells Joey to the British Army, leaving his son heartbroken and putting Joey in horrific danger — more than 8 million horses died during a war that claimed some 17 million human lives. Though he’s too young to fight, Albert lies about his age and secretly enlists, determined to find Joey and bring him home.

The story has myriad elements: the unbreakable bond between humans and animals, the terrible price of war, the bravery of two- and four-legged soldiers, life, death, love. But what makes War Horse so thrilling and unforgettable are its Handspring horses.

Kohler and Jones talked with experts in horse behavior, studied horses and videos of them, then went to work. Weighing 120 pounds (vs. half a ton, give or take, for a real horse), the theatrical Joey is fashioned from bent cane, fabric that looks opaque but allows the actor-puppeteers to see out, an aluminum spine for strength, haunting glass eyes, moveable ears, and a mane and tail made of leather-looking Tyvek. The audience always sees the legs of the two performers inside the horse and the third actor operating the head, but because of the design and the way the horse is manipulated — Joey trots, gallops, twitches his ears, seems to breathe — the audience quickly becomes complicit in the play’s make-believe. It doesn’t hurt that several actors actually ride the horses.

Kohler, who observes that what the audience is looking at “is a fairly abstract version of a horse,” remembers the first workshop version of what has become a key dramatic moment in the show. The colt version of Joey falls apart, and the full-sized Joey gallops onto the stage.

“Nick Starr was sitting where baby Joey ‘explodes’ and becomes big Joey. We could see the moment when the executive producer of the National gave War Horse the green light,” Kohler said recently from the duo’s home in Cape Town.

As the horse puppets progressed from simple to astonishing, playwright Stafford adapted his script to give them more stage time.

“The more the horse developed, the more space it demanded,” he said. “It didn’t bother me at all. It felt really exciting.”

The prolific Morpurgo, who calls War Horse “the first decent children’s book I wrote,” is as affected as anyone by the extraordinary Handspring horses and the play the National created.

“The play lets the audience make the intellectual journey to create the real horse. This enables you, if you’re 8 or 80, to imagine as far as you can. It’s much more akin to reading a book,” he said. “When I come out of the play, I feel wrecked. I cry at different times. I can’t cope with the horse rearing up on the [barbed] wire, that scream. It’s a huge cry for peace.”

Jones and Kohler have expanded Handspring because of the success of War Horse, employing 25 people who have thus far turned out some 90 horses for various productions and promotional purposes. Jones said that auditioning actors to perform as Joey or Topthorn is like a master class, starting out with paper puppets and progressing to being inside the horse. Actors, dancers and puppeteers have all been hired, but Kohler said an additional skill is key: “We have to see whether they can suppress their ego, to do what makes the performance right.”

For the National, War Horse has been a gamble that continues to pay off. The show is making the company 3 million pounds (more than $4.6 million) per year, which is half the National’s yearly fundraising goal. And the show’s key players, Starr said, don’t ever eat into its profits.

“The horses are the stars of the show,” he said. “But they don’t ask for a wage increase.”