The undersized but canny American thoroughbred - voted racehorse of the decade for the 1980s - endeared himself to racing aficionados with his brains, tenacity and gameness rather than any showy feat of derring-do.
"Joe doesn't make precipitous moves; he's not about commotion and fanfare," said Greg Ferraro, director of the Center for Equine Health at the University of California Davis and a friend of Harper's. "But, like John Henry, he is tough, persistent and really hard to beat."
Once an icon of Hollywood glamour, the Del Mar Racetrack had lost much of its luster by the time Harper took the reins in 1978. At the time, the aging outdoor track was ranked about 20th among U.S. tracks in various categories, such as daily attendance and daily wagers.
Last year, the Del Mar track ranked No. 1 in daily attendance, No. 2 in daily wagers and No. 5 in purses paid, said Mike Ernst, chief financial officer of the Del Mar Thoroughbred Club, the not-for-profit entity that runs the racetrack at the Del Mar Fairgrounds.
Most credit Harper's blend of showmanship and shrewd marketing for the transformation. For a brief seven-week season - a mere 43 days - Harper presides with grace and style over a racing meet that has become an international draw for everyone from hard-boiled gamblers to the well-heeled glitterati.
Through it all, Harper, who cultivates an easy, self-effacing style, makes it seem effortless.
"You know, you give a party and a bunch of people are coming to your house, so you walk through the house making sure the flowers are right, the bar is set up, the limes are cut, and the dog poo is off the porch," said Harper, 64, president and general manager of the thoroughbred club. "It's the same here."
Anyone who has seen Harper hit the track at 5 a.m., often getting on a horse and walking the racecourse to gauge the quality of the track before bustling off to attend to scores of other tasks, knows the job isn't quite so simple.
Through the years, Harper has overseen an $80 million renovation of the track and steered it through major competitive challenges, including the advent of off-track wagering and the proliferation of casinos.
Then there are the private and public negotiations - union contracts, off-track wagering contracts, legislative committees - and the meetings of various racing boards and associations.
Perhaps the biggest challenge remains enticing potential new racing fans to the track.
That challenge began in 1988, when intertrack wagering became legal in California and fans no longer had to go to a track to make a bet. The shift meant a potential huge upside in wagering, but was offset by lower attendance and less on-track betting, which is more profitable for the racetrack.
In the first year of intertrack wagering, the Del Mar track saw its attendance drop by 25% and on-track betting fall 35%, but profit soared 116%, Harper said.
"So we said 'terrific,' but while we'd never made so much money, we were a little lonely counting it," Harper said.
"Off-track wagering sites don't make new racing fans. You go in and watch a TV - no one cheers; there is no pageantry to the sport." We wanted to create an atmosphere that made people want to come to the racetrack, not just stay home and bet."
Harper and his staff set about building up the on-track business, instituting a variety of nonracing activities - including a concert series that has drawn as many as 12,000 fans for a single show, and the One and Only Truly Fabulous Hats Contest, now an opening day tradition.
"This isn't the gambling business. It isn't the restaurant business. This is the entertainment business," Harper said. "Whenever you put 40,000 people into a facility, you better make them happy, and the only way to do that is to entertain them.
"Whether it's with racing or beautiful people or $11 margaritas, you have to have them feeling good about being here."
Harper is an expert at the entertainment business. In his 20s and early 30s, he was a successful Hollywood cinematographer and, as the grandson of legendary director Cecil B. DeMille, was a child actor in some of his grandfather's most lavish spectacles, including "The Ten Commandments" and "The Greatest Show on Earth."
Harper recalls how, as an 11-year-old, he sat on a ladder with Cary Grant watching Charlton Heston toss a pair of fake stone tablets at a group of extras who were doing "something I didn't quite understand to a golden calf."
Harper lived at his grandfather's compound in the Hollywood Hills with his parents, Joseph W. Harper Sr., an executive at a leading Hollywood production company, and his mother, Cecilia DeMille Harper, a prominent horsewoman who bred thoroughbred horses at Middle Ranch, a 1,000-acre family ranch.
It was an exciting childhood, but it also could be a tough one. Harper often was sent to boarding schools or holiday camps as his parents and grandfather pursued busy careers.
Yet what might have been a celebrity offspring recipe for lifelong therapy and substance abuse never materialized. Instead, Harper passed his childhood as "part mascot, part pain-in-the-arse" to the DeMille household staff, which included a Romanian cook, a Finnish maid, a German housekeeper, a Scottish valet, a Russian gardener and an American chauffeur.
Harper said he loved his "kitchen family," and lunchtime around the kitchen table with the staff "looked and sounded like the commissary at the United Nations."
On weekends, if no family members were home, Harper stayed in the homes of Stanley Russell, the chauffeur, who had a pet alligator in the backyard, or with Hedwig Gottwald, the housekeeper, who lived with her cobbler husband in a tiny, yellow house near the Los Angeles River.
By the time he was 10, Harper said he could "read tea leaves, bake a popover, iron a shirt and wax a limo."
"I grew up in the kitchen, and it was a wonderful place to grow up," Harper said. "I always felt love, always had hugs, and I always had loving people around me, whether it was the cook and the housekeeper, or Mom and Dad."
Yet when it came time to raise his four daughters with his wife, Barbara, Harper made sure that there was no Christmas camp.
"I was always, 'You don't want to go to camp, right?' or 'You don't want to go to boarding school, right? You want to stay home, right?,'" Harper said. "When our eldest daughter was about eight she spent the night with a friend, and she called in the middle of night wanting to come home. I couldn't drive fast enough to get her because I knew how it felt."
Elizabeth Hartzog, the second of the Harpers' children, said the home was "a great one to grow up in."
"All of our friends were always at our house; a couple of kids whose parents were going through divorces even lived with us for a time - it was that kind of home," said Hartzog, the mother of three of the Harpers' nine grandchildren. "I sort of understand my mom's plight now that I have children. Ice cream for breakfast. Roughhousing and crazy times when it 'feels right.'
"Our father was not one for a lot of rules, just a lot of love. He's a kid. He totally relates to the 8-, 9-, 10-year-old at many levels."
Hartzog said she recently asked her father what he would like to be if he could come back in another life. His impish reply: "One of my own children."
"I said, 'That's pretty conceited - but pretty true,'‚" Hartzog said with a laugh.
Harper's friends and colleagues speculate that his eclectic childhood helped shape a singularly egalitarian viewpoint. Harper doesn't have a snob bone in his body, they say.
"A lot of people wear success on their sleeve, the $5,000 Armani coat, but Joe couldn't give a rat's butt," said Markus Heon, Harper's personal trainer for 12 years. "He wants to see things run smoothly and to be kind to people."
Another leading Harper characteristic is a devastating sense of humor, friends and colleagues say.
"I think it comes from living in a celebrity environment where everyone is very good at what they do, and probably a defense mechanism he developed to cope with the challenging environment of his youth," said Dr. Stephen Dorros, a clinical professor of radiology at University of California San Diego and longtime friend of Harper's. "But he's just a 100%, innately funny guy, and that's a challenge for his friends because no one can ever be as funny and cool as Joe."
Harper credits racetrack cinematographer Joe Burnham, with whom he worked as an assistant for 11 years before landing his first job in racetrack management in 1971, with shaping him in his adult years.
"Cameras have a tendency to strip away pretense, and you see more of human nature than you might through a casual conversation," Harper said. "Through a camera, you learn to look a little deeper into people, and when you do that you find out that you really like someone or maybe they aren't quite as good as you thought. Joe Burnham taught me that."
When the opportunity came to run a racetrack, Harper said he decided that he wanted to be part of something that was "all about relationships, about being honest, forthright, smart and all those things you hope will get you somewhere."
"So I went for it and hung up the camera," Harper said. Then, with a laugh, he added, "But I always kept up my payments on my union card - just in case."