Killed were Timothy Treadwell, 46, and Amie Huguenard, 37, both of Malibu, California, said the National Park Service and the Alaska State Troopers.

Treadwell was the founder of Grizzly People, an organization devoted to the protection of grizzly bears and their habitat. According to the group's Web site, Treadwell's practice was to travel to bear country without weapons.

Treadwell, a former drug addict, was featured on the Web site of actor and environmental activist Leonardo DiCaprio. According to a biography on the site, Treadwell beat his addiction by spending time in the Alaskan wilderness, where he developed his fondness for bears.

The co-author of a book entitled "Among Grizzlies: Living with Wild Bears in Alaska," Treadwell appeared on the "Late Show with David Letterman" and traveled the country to lecture on the bears and their environment.

It was the first fatal bear attack in Katmai for at least 15 years, the Park Service said. The park is known as one of the world's premier sites for viewing huge brown bears, the coastal cousins of grizzlies, as they feast on salmon.

The deaths were discovered when an air-taxi pilot flew to the site Monday afternoon to pick up the campers. He found the campsite damaged and a brown bear atop what appeared to be a human body, eating the remains.

When park rangers and state troopers flew to the remote site to recover the bodies, they had to kill two aggressive bears that were threatening them, officials said.

The Park Service has closed the area to visitors and is investigating the deaths.

The service had cautioned Treadwell for several years about his bear-safety practices, spokesman John Quinley said.