Just so we're clear: this is the gorge of the Little Colorado River, which is a tributary of the Colorado River; and the Colorado River, as most of our readers will know, is the one that flows through the Grand Canyon.
Nik Wallenda is a seventh-generation member of the family circus act known as the Flying Wallendas. His crossing of the Little Colorado River Gorge was billed as "a Grand Canyon Crossing", even though it would be more accurate to describe it as "a crossing of a river gorge in the Grand Canyon region".
This wasn't even his best known stunt; according to Wikipedia, Nik Wallenda is "best known as the first person to walk a tightrope stretched directly over Niagara Falls." Even so, I would suggest that his name is not that well known on this side of the Pond, and this is probably one of the more difficult questions on a night that wasn't memorable for its high scoring.
The significance of Wikipedia's words "stretched directly over Niagara Falls" is that the French tightrope walker Charles Blondin (real name Jean François Gravelet) crossed the Niagara River on a tightrope in 1855. But Blondin made his crossing a couple of hundred yards downstream from the Falls, near the current location of the Rainbow Bridge.
I'd have preferred to be asked who was the first man to cross Niagara Falls on a tightrope. You would have to allow either Wallenda or Blondin, and I bet most people would have answered Blondin; but I don't really see any problem with that.
© Macclesfield Quiz League 2019