Doug Peacock served two tours in the Vietnam War as a medic with the U.S. Army Special Forces. To find peace, he spent much of the time imagining he was somewhere else—Yellowstone National Park.

When he got back, he sought solitude there, and lived amongst a landscape that he’d previously only dreamed about. He soon encountered grizzly bears, and as he got to know these creatures, he came to respect and love them. They changed his life forever.

Peacock, who is the real-life basis for the character George Hayduke in his friend Edward Abbey’s book, The Monkey Wrench Gang, has since devoted the last half-century to writing about and advocating for the grizzly bear, which remains a threatened