The first free solo climb of the south wall of El Capitan, in Yosemite National Park, Calif., was by climber Dean Potter. Potter, 39, also slacklines and BASE jumps. He is profiled on 'The Man Who Can Fly,' premiering Sunday, February 12, at 8 PM ET/PT on National Geographic Channel.

Clutching El Capitan, Dean Potter "free climbs" -- meaning, with no ropes or safety harness -- in Yosemite National Park, California. Potter holds records for free climbs on some of the world's tallest mountains.

Chuck Burchill's workshop at Homathko Camp in Mt. Bute, British Columbia. Dean Potter pursued a quest, documented in the National Geographic program, to launch off the 9,000-foot Mount Bute in his wing suit.

Culminating his quest, Dean Potter dives head first off the side of Mt. Bute, in British Columbia, hoping to reach speeds over 120 miles per hour. Potter holds a record for the longest flight in a suit that essentially mimics a flying squirrel. It was off the 13,000-foot Eiger, in Switzerland.

"In some way, I wonder if it's healthy what I do," Potter told ABC News. I'm not even trying to say what I do is good. I go back and forth to asking myself those questions. Dean, man, is this healthy? You're obsessed on this thing that might kill you."

The view from Potter's expedition tent on top of Mt. Bute, in Mt. Bute, British Columbia. Asked what scares him, Potter replied, "Normal stuff is harder for me. I definitely struggle with everyday stuff for other people like balancing my checkbook or paying my taxes on time."

Leaping head first, Dean Potter soars to meet the ocean in Mt. Bute, British Columbia. Potter insists he's no thrill seeker. He calls himself an artist. And, despite -- or because of -- his rejection of safety gear, Potter says he's very cautious, often turning back from climbs or jumps.

Potter and his faithful companion, Whisper, take in the view at Turtle Back Dome in Yosemite National Park in Yosemite National Park, California. Yosemite is Potter's home base.

Reaching speeds over 100 miles per hour, Potter flies in his newly designed and enhanced wingsuit in Mt. Bute, British Columbia. Potter is working to become the first to land without a parachute, instead just slowing himself down with the suit.

Potter gives fellow BASE jumper Wayne Crill some instructions near a cliff edge before Wayne's first wingsuit jump, in Squamish, British Columbia.

Yosemite National Park, Yosemite, Calif.: Potter walks a highline. "I'm forced to think about my mortality," Potter said. "I don't want to die until I'm an old, old man. ... I absolutely don't want to die falling. ... I am very afraid of that. But somehow I have an even deeper draw within me to keep going towards my fears."

Dean Potter meditates in a field outside the Flight Lab at The University of Montana in Missoula, Mont., as birds fly around him. Potter's friend Dean Fidelman said, "Dean is looking for the experience. He's looking for a barrier that he can push himself beyond. I don't think he's looking to prove himself to himself; I think he's looking to introduce himself to himself."

Potter makes the first ropeless ascent up the south face of El Capitan, in Yosemite National Park, Yosemite, Calif. "When your life is on the line, your whole being pours all of its energy into surviving. And what it takes to survive is focus and relaxation. And it was hard for me to do that until I got my feet way above the ground and had to focus to survive."

Tony Uragallo, of Tony Suits, and Potter soar above Zephyrhills, Fla. WATCH THE FULL STORY ON 'NIGHTLINE' TONIGHT AT 11:35/10:35C.