Instructor Linda Nelson helps Isabel Kessler while Jackson, the horse, is shown on the left. The program at the Rock Creek Park Horse Center brings together children with volunteers for therapeutic riding. (Michael DiBari Jr./Washington Post file)

He came to Washington 15 years ago, an appaloosa with a graying face, speckled hindquarters, a sketchy past and iffy medical records.

He loathed men. And when the region’s expert riding instructors mounted him, he bucked them off.

It was children Jackson adored, and until his death last week, hundreds of them learned to ride on his powerful back at the Rock Creek Park Horse Center.

“He was the sweetest thing, sweet because he ate sugar and sweet because he was so gentle,” explained Bridget Keon, 8, who rode Jackson in one of his last shows.

“He was the gentle giant,” cooed Nadia Langer, 12. “He was my first horse.”

Jackson, after being dressed up by kids. (Courtesy of Nicky Beveridge)

See, for Bridget, Nadia and legions of other little people who passed through the park’s riding school, Jackson had a different personality.

“Kids, he wanted kids to ride him. He was very, very clear about that,” said Amber Power-Shickler, general manager of the stables and humble servant to Jackson’s very particular wishes.

Power-Shickler never once rode him. “I knew better,” she said. “But I put my 6-year-old son on him all the time.”

Jackson was probably abused in his earlier years and likely by a man, the staff at the stable surmised, when they watched Jackson reject rider after rider.

So maybe it was understandable that Jackson was the go-to schoolie horse, his furry, dexterous lips always gently choosing the carrots, not the fingers, and his soft bray a reward for a ride well-done.

He was the horse who always took the frightened, the small and the nervous children. He had a pitch-perfect trot for kids, and somehow the intuition to know just when to go a little harder, a little softer, to lean one way or another to balance the newbie rider, without the help of expert grown-ups, thank you.

Eventually, the staff learned that Jackson allowed a very select group of adults on his back, too — the injured and disabled. He tossed able-bodied riders, but had a soft spot and special intuition for carrying wounded troops or adults with cerebral palsy.

Jackson (courtesy of Nicky Beveridge)

The horse had a special relationship with Christoph Ruesch, 29, who can move only his neck and head. Jackson became Christoph’s muscular chest and strong legs so that for one hour a week, Christoph could move among the trees, 10 feet tall, striding with a swagger.

Jackson launched a thousand riders. And while he seemed to turn into a 1,000-pound, rodeo mustang whenever an experienced adult mounted him, he held perfectly still for the annual costume party, when a few dozen little hands swarmed all him, and they would dress him up like a knight or a fairy or a Solid Gold dancer in a gold lamé cape. He would turn his neck just so, to emphasize the tilt of his huge fedora.

They say animals don’t, but I saw the pictures. He was totally smiling.

When Jackson began to age and show signs of pain, the staff tried to retire him, cutting his schedule off and letting him rest. They didn’t know when, exactly, he was born, but guessed that he was 33, which is older than the average 30-year life span for an appaloosa.

He grew depressed, hanging his head and facing the rear of his stall, turning his graying back on the world. It wasn’t until they put a child on his back that he perked up.

“He clearly needed them. He knew what his job was, and he wanted to do it,” Power-Shickler said. “So we let him.”

This horse gave Washington — a city filled with ambition and ego — a lesson in what it takes to create a legacy.

Up until three weeks before his death, Jackson kept up a three-hour riding schedule, flicking his tail and holding his head high throughout his final canter. After the entire staff held him for the vet’s invasive exam, and the doctor’s head shake told them Jackson wasn’t going to make it, they had another problem.

They had to break the news to hundreds of children, teens and young adults that Jackson was gone. It took two days for the staff to find the right words to tell anyone. The instructors announced his passing in e-mails and on Facebook, where memories and tributes instantly began rolling in.

“He was always the heart” of the horse center, one young woman mourned.

Shannon Bieter learned the news by e-mail, so she had a chance to compose herself before telling her daughter, Vivian.

“We just went through it with our dog, so I was kind of ready with a talk,” Bieter said. “I told her how every time she rides, Jackson’s spirit rides with her.”

At her lesson this week, Vivian rode Munchie, her other favorite horse. She’ll miss Jackson, but she’s certain he’s romping in horse heaven.

“When my mom told me, I cried a little. But now I know he’s happy and safe up there,” she told me.

The staff is planning a memorial service for Jackson, and they expect it to be packed. A drill team is already practicing a routine to honor him.

Power-Shickler and her children will be there. Jackson was one of their favorites, too. So how did she break the news to them that the horse was gone?

“I have to admit, they still don’t know,” she said. ”It’s just so hard when it’s someone so special.”

Follow me on Twitter: @petulad.