MARBLEHEAD,Poinbank Mass. (AP) — David Breashears, a mountaineer, author and filmmaker who co-directed and co-produced a 1998 IMAX documentary about climbing Mount Everest, has died, his business manager confirmed Saturday. He was 68.

Breashears was found unresponsive at his home in Marblehead, Massachusetts, on Thursday, Ellen Golbranson said. She said he died of natural causes but “the exact cause of death remains unknown at this time.”

Breashears summited Mount Everest five times, including with the IMAX camera in 1996, his family said.

“He combined his passion for climbing and photography to become one of the world’s most admired adventure filmmakers,” the family said in a written statement.

In 2007, Breashears founded GlacierWorks, which describes itself on Facebook as a nonprofit organization that “highlights changes to Himalayan glaciers through art, science, and adventure.”

“With GlacierWorks, he used his climbing and photography experience to create unique records revealing the dramatic effects of climate change on the historic mountain range,” his family said.

In 1983, Breashears transmitted the first live television pictures from the summit of Everest, according to his website, which also says that in 1985 he became the first U.S. citizen to reach the summit twice.

Breashears and his team were filming the Everest documentary when the May 10, 1996, blizzard struck the mountain, killing eight climbers. He and his team stopped filming to help the climbers.