Extreme athlete Dean Potter, renowned for his bold climbs and Base jumps, was one of two men killed while attempting a wingsuit flight in Yosemite National Park.

One of his team called for help after losing contact with Potter, 43, and his climbing partner, Graham Hunt, 29.

They had jumped from a 7,500-ft promontory called Taft Point, park ranger Scott Gediman said.

A helicopter crew spotted their bodies in Yosemite Valley. No parachutes had been deployed.

The sport of Base jumping is illegal in all national parks, and it was possible the men jumped at dusk or at night to avoid being caught by park rangers.

Potter and Hunt, who lived near Yosemite, were prominent figures in the park's climbing community, Mr Gediman said.

"This is a horrible incident, and our deepest sympathies go out to their friends and family," he said. "This is a huge loss for all of us."

Potter was famous for pushing the boundaries of climbing by going up some of the world's most daunting big walls and cliffs alone, using his bare hands and without ropes.

He took the sport to an extreme level with highlining - walking across a rope suspended between towering rock formations while wearing a parachute for safety in the event of a fall.

He drew criticism in May 2006 after he made a "free solo" climb of Utah's Delicate Arch in Arches National Park.

Though the climb was not illegal, outdoor clothing company Patagonia dropped its sponsorship of him, saying his actions "compromised access to wild places and generated an inordinate amount of negativity in the climbing community and beyond".

Potter defended his ascent, saying his intention was to inspire people to "get out of their cars and experience the wild with all their senses".

In more recent years, he combined his love of climbing and flying with Base jumping. He also produced a film that chronicled his adventures Base jumping with his dog Whisper.

In 2009, he set a record for completing the longest Base jump from the Eiger North Face in Switzerland by staying in flight in a wingsuit for 2 minutes and 50 seconds. The feat earned him the Adventurer of the Year title from National Geographic magazine.

A photographer who documented that jump, and knew Potter for more than 15 years said Potter stood out from other climbers not only for his skills but his boldness.

Corey Rich said: "On one level, you lose a friend. But it's also difficult to be surprised because Base jumping is the most dangerous thing you can do. The odds are not in your favour, and sadly Dean pulled the unlucky card."