The cause was not immediately known, said his daughter, Gail Selby Wentink.
Mr. Selby shot his first antelope at 8, killed his first elephant at 14 and became one of the most famous hunters in the world soon after his 28th birthday, when he organized an East African safari for syndicated columnist Robert Ruark.
A protege of Philip Percival, a guide who was known as the "dean of hunters" and credited as an inspiration for stories by Ernest Hemingway, Mr. Selby spent two months in the bush with Ruark and the writer's wife and children, tracking lions by foot and outmaneuvering herds of stampeding wildebeest.
The 1953 expedition resulted in Ruark's writing a popular travelogue, "Horn of the Hunter" (1953), and helped inspire his novel "Something of Value" (1955), which featured a lightly fictionalized version of Mr. Selby — Peter McKenzie, a sharpshooter whose "lips curved down in scorn at the idea of hunting anywhere that other men hunted."
For romantics who had never stepped foot in Africa, Mr. Selby was seen as a paragon of masculinity, a swaggering man of derring-do whose heroics with a .416 Rigby rifle were the real-life counterpart to those of film actors who portrayed men of action on the savanna, including Clark Gable and Stewart Granger.
"Every woman he meets wants to mother or marry him and every man respects him," Ruark reported in one column. "I have seen him slap a lion in the face with his hat. I have seen him hide from a woman. His business is killing."
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Mr. Selby undoubtedly excelled at the latter, helping his clients track and shoot thousands of elephants, lions, leopards, buffalo, impala, wildebeest, sable antelope and fowl.
But he did so with little fanfare, acquiring a professional reputation as a charming, courteous and even diplomatic host to hunters and photographers, camera-wielding thrill seekers who came to form a significant portion of his clientele.
Wildlife aficionados he guided included scores of anonymous hunters, wealthy industrialists and a sprinkling of royalty: Prince Bernhard of the Netherlands, oil-family scion John Mecom Jr., baseball executive Walter O'Malley, opera singer Lauritz Melchior, the maharajah of Jaipur, Prince Stanislaw Radziwill of Poland and Miguel Alemán Valdés, a former president of Mexico.
"It is my duty and responsibility to treat each client as though he were a gentleman," Mr. Selby told People magazine in 1976, "no matter what sort of spectacle he may make of himself."
Working primarily with the Nairobi-based outfit Ker, Downey & Selby, he organized expeditions in Kenya before moving to Maun, then part of the British protectorate of Bechuanaland, around 1963. Once home to just a few thousand people, the town is now a tourist gateway to Botswana's wildlife-rich Okavango Delta and a short flight or drive from the Kalahari Desert to the south.
Mr. Selby acquired a hunting concession of about 4,500 square miles — "larger than many African national parks," the New York Times reported in 1970 — and with his company helped build the wildlife-tourism industry in Botswana, blazing new trails through the bush and building some of the country's first lodges for wildlife photographers.
While Botswana's northern swampland was ridden with disease-carrying tsetse flies and malaria, Mr. Selby and his clients traversed the bush in style. Their campsites were pitched by a dozen porters and featured separate tents for the showers and bathroom, a refrigerator, and tables set with linens and silverware.
Early in his career, Mr. Selby and his team spent days building bridges or crossing riverbeds in the backcountry, sometimes emptying their vehicles of oil and fuel — and disconnecting the battery — before using rope to tow their submerged cars across rivers.
He once successfully administered antivenin to a skinner who had been bitten by a snake, he wrote in a column for Sports Afield, and soldered a leaking radiator on a baggage truck. Because there was no wood, he heated the soldering iron — and the night's dinner — "in a fire made of wildebeest dung."
On another occasion, Mr. Selby worked to assist a duchess in photographing a camera-shy rhino. She climbed a tree in search of a better view, Ruark later reported, and soon saw Mr. Selby running toward the tree himself, the rhino racing behind him.
"If you please, your grace," Mr. Selby was said to have asked, "would you mind moving up another branch?"
John Henry Selby was born in Frankfort, South Africa, on July 22, 1925. His family moved near Nanyuki, Kenya, to start a cattle farm when he was a boy. A left-handed shooter who preferred right-handed weapons, Harry — as he was known since childhood — began hunting with a Browning .22 rifle as a way to protect the farm's crops and cattle from predators.
He started leading professional hunts in 1945, according to his friend and former apprentice Joe Coogan, and in the 1950s contributed his tracking abilities to Kenya's colonial government, which enlisted him in fighting rebels during a revolt known as the Mau Mau uprising. His departure from the country coincided with Kenya's independence in 1963.
Mr. Selby remained in Maun through his retirement from professional hunting in 2000, and for years kept the house bereft of hunting trophies, save for a large Kodiak bear he had shot in Alaska. "A lamp fashioned from the drumstick of an ostrich," he told People, "strikes me as rather gauche."
Survivors include his wife of 65 years, the former Maria Elizabeth Clulow, a onetime flight attendant who goes by Miki; his daughter, Selby Wentink of Maun, an operations manager for the photographic outfit Machaba Safaris; three grandchildren; and two great-grandchildren. A son and fellow hunter, Mark Selby, died last year.
While Mr. Selby began hunting at a time when restrictions were few and lions were considered "vermin," he made animal conservation a centerpiece of his business early on. In 1970, the Times reported, he had cut the number of animal hunts his company led each year from 40 to 30 and predicted — accurately — that his industry's "real future will be in nonhunting tourism," especially in photography.
Still, he never entirely moved away from hunting, a sport that he described in near-spiritual terms.
"To deny the instinct to hunt," he told People, "is to deny the instinct to exist."
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