Longtime friend and promoter Billy Rundel says Knievel had trouble breathing at his Clearwater condominium and died before an ambulance could get him to a hospital.
The hard-living motorcycle daredevil, renowned for jumps over Greyhound buses, live sharks and Idaho's Snake River Canyon, was an international icon in the 1970s.
Immortalized in the Washington's Smithsonian Institution as "America's Legendary Daredevil," Knievel was best known for a failed 1974 attempt to jump Snake River Canyon on a rocket-powered cycle and a spectacular crash at Caesar's Palace in Las Vegas. He suffered nearly 40 broken bones before he retired in 1980.
Although he dropped off the pop culture radar in the '80s, Knievel always had fans and enjoyed a resurgence in popularity in recent years. In later years he still made a good living selling his autographs and endorsing products. Thousands came to Butte, Mont., every year as his legend was celebrated during the "Evel Knievel Days" festival.
"They started out watching me bust my ass, and I became part of their lives," Knievel said. "People wanted to associate with a winner, not a loser. They wanted to associate with someone who kept trying to be a winner."
For the tall, thin daredevil, the limelight was always comfortable. To Knievel, there always were mountains to climb, feats to conquer.
"No king or prince has lived a better life," he said in a May 2006 interview with The Associated Press. "You're looking at a guy who's really done it all. And there are things I wish I had done better, not only for me but for the ones I loved."
He had a knack for outrageous stories: "Made $60 million, spent 61. ...Lost $250,000 at blackjack once. ... Had $3 million in the bank, though."
Born Robert Craig Knievel in the copper mining town of Butte, Mont., on Oct. 17, 1938, he was raised by his grandparents after his mother and father divorced. He got into trouble frequently with the law in his youth, sometimes with a motorcycle involved (though he also got flack for popping a wheelie with an earth mover when he worked for a mining company).
At various times and in different interviews, Knievel claimed to have been a swindler, a card thief, a safe cracker, and a holdup man.
Knievel served in the Army, ran his own hunting guide service, and owned dealerships selling Honda motorcycles, where he drummed up business by offering $100 off the price of a motorcycle to customers who could beat him at arm wrestling.
After his hunting and sales businesses closed, and despite achieving some success as an insurance salesman, in the 1960s Knievel decided try his hand at motorcycle stuntwork to make a living. He traced his inspiration to the time he saw Joey Chitwood's Auto Daredevil Show at age 8.
He began his daredevil career in 1965, when he formed a troupe called Evel Knievel's Motorcycle Daredevils, a touring show in which he performed stunts such as riding through fire walls, jumping over live rattlesnakes and mountain lions and being towed at 200 mph behind dragster race cars.
In 1966 he began touring alone, barnstorming the U.S. West and doing everything from driving the trucks, erecting the ramps and promoting the shows. In the beginning he charged $500 for a jump over two cars parked between ramps.
He steadily increased the length of the jumps until, on New Year's Day 1968, he was nearly killed when he jumped 151 feet across the fountains in front of Caesar's Palace. He cleared the fountains, but the crash landing put him in the hospital in a coma for a month.
His son, Robbie, successfully completed the same jump in April 1989.
In the years after the Caesar's crash, the fee for Evel's performances increased to $1 million for his jump over 13 buses at Wembley Stadium in London - the crash landing broke his pelvis - to more than $6 million for the Sept. 8, 1974, attempt to clear the Snake River Canyon in Idaho in a rocket-powered "Skycycle." The money came from ticket sales, paid sponsors and ABC's "Wide World of Sports."
The parachute malfunctioned and deployed after takeoff. Strong winds blew the cycle into the canyon, landing him close to the swirling river below.
On Oct. 25, 1975, he jumped 14 Greyhound buses at Kings Island in Ohio.
Knievel decided to retire after a jump in the winter of 1976 in which he was again seriously injured. He suffered a concussion and broke both arms in an attempt to jump a tank full of live sharks in the Chicago Amphitheater. He continued to do smaller exhibitions around the country with his son, Robbie.
Many of his records have been broken by daredevil motorcyclist Bubba Blackwell.
Knievel also dabbled in movies and TV, starring as himself in "Viva Knievel" and with Lindsay Wagner in an episode of the 1980s TV series "Bionic Woman." George Hamilton and Sam Elliott each played Knievel in movies about his life.
Evel Knievel toys accounted for more than $300 million in sales for Ideal and other companies in the 1970s and '80s.
Evel Knievel married hometown girlfriend, Linda Joan Bork, in 1959. They separated in the early 1990s. They had four children, Kelly, Robbie, Tracey and Alicia. Robbie Knievel followed in his father's footsteps as a daredevil.
Knievel had 10 grandchildren and a great-grandchild.
Knievel lived with his longtime partner, Krystal Kennedy-Knievel. They married in 1999 and divorced a few years later but remained together.
His granddaughter, who confirmed his death today, said he had been in failing health for years, suffering from diabetes and pulmonary fibrosis, an incurable condition that scarred his lungs.
Knievel had undergone a liver transplant in 1999 after nearly dying of hepatitis C, likely contracted through a blood transfusion after one of his bone-shattering spills.
His death came just two days after it was announced that he and rapper Kanye West had settled a federal lawsuit over the use of Knievel's trademarked image in a popular West music video.