When Nik Wallenda walks a high wire across Niagara Falls, continues a family tradition that dates back centuries.
"People say I'm insane all the time, but they don't understand that this is something I've done since I was 2. It's just in my blood," he said.
Wallenda is a seventh-generation member of the Great Wallendas, a travelling family circus troupe. He traces his family's performance history back to 1780s Europe, during the era of the Austro-Hungarian empire.
His ancestors made up a traveling circus of acrobats, aerialists, animal trainers, clowns and jugglers. By the late 1800s, the family became known for its flying trapeze stunts.
Nik Wallenda's great-grandfather, the man who would become the most legendary Wallenda, was born in 1905 in Magdeburg, Germany. Karl Wallenda performed in his family's shows at age six, eventually specializing in doing handstands upon stacked chairs. He learned wire-walking as a teen and later recruited people to form his own act. One of his recruits, a teenage girl named Helen Kreis, later became Karl Wallenda's wife.
Karl Wallenda and his team began performing a jaw-dropping four-person, high-wire pyramid: two men sitting on bicycles on a tightrope held a bar upon which Karl Wallenda balanced on a chair while Helen stood on his shoulders. The act impressed John Ringling of the Ringling Brothers Circus, who invited the family to perform in the United States in the 1920s, where they settled.
By 1947, Karl Wallenda had raised the stakes: he expanded his high-wire pyramid from four people to seven, with four men on a wire making up the pyramid's base level, two men in the middle and a woman standing on a chair at the top.
The act was performed successfully until 1962, when tragedy struck. During a performance in Detroit, the pyramid collapsed. Two family members plunged to their deaths and Karl Wallenda's son, Mario, was paralyzed.
Karl Wallenda was also injured and hospitalized, but he didn't stay in a hospital bed for long.
"He snuck out of the hospital because they wouldn't release him with broken bones so he could go up and perform the next show," Nik Wallenda said.
Nik Wallenda's mother and Karl Wallenda's grandaughter, Delilah Wallenda Troffer, remembers her grandfather's resilience.
"What he said was, 'We still have to keep, take care of the living. The dead are gone. We have to keep going,' " she recalled.
In July 1970, Karl Wallenda performed one of his most memorable stunts, walking a tightrope 750 feet up in the air above Georgia's Tallulah Falls Gorge.
"He would go out to the middle and do a headstand," Nik Wallenda said. "There, he happened to do two, and I'm sure his thoughts were, 'This is taking so long. I've got to do something to keep the audience entertained.'"
Nik Wallenda's mother and father, Delilah Wallenda Troffer and Terry Troffer, toured the world with Karl Wallenda.
Nik Wallenda said he grew up on a wire.
"My first memory of being on the wire was in my parents' backyard about two feet off the ground and just playing, just having fun," he said.
By age 13, Nik Wallenda was performing professionally. Eventually, he met a fellow performer who would become his wife -- an eighth-generation acrobat named Erendira.
The couple have three children and, at their Florida compound, all three have walked the wire.
The older generations of Wallendas continue to walk the wire, too, including Nik Wallenda's mother, Delilah Wallenda Troffer, now 59, his uncle Tino Wallenda, 61, and Jenny Wallenda, 84, Karl Wallenda's daughter.
Karl Wallenda died at age 73 in Puerto Rico during a high-wire walk between two hotels on a windy day in 1978. The Wallenda family says he fell after a rig had not been properly stabilized and, as an older man, it was an obstacle Karl Wallenda just couldn't overcome.
"He just didn't have the strength to hold on," Nik Wallenda said. "If he had the strength, if it was 20 years before, he'd be alive to this day."
Last year, Nik and Delilah Wallenda Troffer did the same walk in honor of Karl Wallenda for the Science Channel's show, "Danger by Design," on the Science Channel premiering on June 18.
"I walked out right to where my great grandfather fell and I knelt down, and I looked up and blew him a kiss," Nik Wallenda said.
"I'm sure that he looked down and kind of gave me a wink," he said. " At seven generations, just because we've had some tragedy, we're not going to give up that easily. ... I know that he is up there and he's very, very proud."