Knievel had suffered ill-health, including diabetes and pulmonary fibrosis - an incurable lung condition - for several years.
He underwent a liver transplant, after nearly dying of hepatitis C, in 1999.
Knievel gained cult status performing death-defying stunts in the 1960s and 70s, including an attempted motorcycle jump over Snake River Canyon in Idaho.
HAVE YOUR SAYHe was such a mythical and iconic figure that later on, as a teenager, I had to be convinced he wasn't some made-up figure from a distant childhood memory.
Marc Starr, Manchester
He regularly drew huge crowds when he attempted to jump over rows of parked vehicles with his motorbike.
"They started out watching me bust my ass, and I became part of their lives," Knievel once said.
In one famous incident in 1968, he attempted to jump over the fountains at the Caesars Palace casino in Las Vegas.
The resulting crash put him in a coma for 29 days, but brought him a large amount of publicity.
His 1974 attempt to cross the Snake River Canyon in Idaho on a rocket-powered bike also failed, when a parachute opened prematurely and he fell into the river.
By the time he retired in 1980 Knievel had broken nearly 40 bones.