Timothy Treadwell studied grizzly bears during summer seasons for 13 years, before being killed by one of them. According to his book, Among Grizzlies: Living with Wild Bears in Alaska, his mission to protect bears began in the late 1980s after surviving a heroin overdose. He claims in his book that his drug addiction grew from his alcoholism. A lover of animals since he was a child, he traveled to Alaska to watch bears after a close friend convinced him to do so. He wrote that after his first encounter with a wild bear, he knew he had found his calling in life, and that now his destiny was entwined with that of the bears. He attributed his recovery from drug and alcohol addictions entirely to his relationship with bears. Timothy Treadwell spent the early part of each season camping on the “Big Green”, an open area of bear grass in Hallo Bay. on the Katmai Coast. He called the area “The Grizzly Sanctuary”. Treadwell was known for getting extremely close to the bears he observed, sometimes even touching them and playing with bear cubs. However, in his book, he claimed that he was always careful with the bears and actually developed a sense of mutual trust and respect with the animals. He habitually named the bears he encountered and consistently saw many of the same bears each summer, and thus claimed to build a standing relationship with them. In contrast, National Park Service Rangers said he was harassing wildlife. During the later part of each summer he would move to Kaflia Bay and camp in an area of especially thick brush he called the “Grizzly Maze”. Here the chances of crossing paths with grizzlies were much higher, since the location intersected bear trails. Treadwell recorded almost 100 hours of video footage (some of which was later used to create the documentary Grizzly Man) and produced a large collection of still photographs.

Timothy Treadwell claimed to be alone with the wildlife on several occasions in his videos. However, his girlfriend Amie was with him during parts of the last three summers (the documentary says two summers) and at the time of his death. It is further noted that several women, who wish to remain anonymous, accompanied Treadwell during various summers over 13 years. By 2001, Treadwell became sufficiently notable to receive extensive media attention both on television and in environmental circles, and he made frequent public appearances as an environmental activist. He traveled throughout the United States to educate school children about bears and appeared on the Discovery Channel, the Late Show with David Letterman, and Dateline NBC to discuss his experiences. He also co-authored Among Grizzlies: Living with Wild Bears in Alaska with Jewel Palovak (his co-worker with whom he lived for 20 years), which describes Treadwell’s adventures on the Alaska Peninsula. Treadwell and Palovak founded Grizzly People, an organization devoted to protecting bears and preserving their wilderness habitat. Charlie Russell, who studied bears, raised them, lived with them in Kamchatka, Russia, for a decade, and worked with Treadwell, wrote a lengthy critique of Treadwell’s lack of basic safety precautions, such as pepper spray and electric fences. He also commented on what he considered the standard reaction of Alaskans to hearing of Treadwell’s death, writing, “If Timothy had spent those thirteen years killing bears and guiding others to do the same, eventually being killed by one, he would have been remembered in Alaska with great admiration.” Russell was also critical of the film Grizzly Man, saying it was inaccurate, and if Palovak “really was a protector of bears, she should have looked for a filmmaker who would have been sympathetic towards them.”

According to the organization Timothy Treadwell founded, Grizzly People, five bears were poached in the year following his death, while none had been poached while he was present in Katmai. However, according to court records as reported by the Anchorage Daily News, the guilty parties were charged with poaching wildlife along Funnel Creek in the Preserve, an area open to hunting that borders the National Park. According to several sources, including Nick Jans’ book, The Grizzly Maze, Treadwell only camped near the Katmai Coast, mainly in areas around Hallo Bay and Kaflia Bay, and never in or near the Preserve. The only effective way to patrol all 6,000 square miles (16,000 km2) of Katmai National Park is by airplane, the method used by authorities. Around noon on Sunday, October 5, 2003, Timothy Treadwell spoke with an associate in Malibu, California, by satellite phone; Treadwell mentioned no problems with any bears. The next day, October 6, Willy Fulton, the Kodiak air taxi pilot, arrived at Treadwell and Huguenard’s campsite to pick them up but found the area abandoned, except for a bear, and contacted the local park rangers. The couple’s mangled remains were discovered quickly upon investigation. Treadwell’s disfigured head, partial spine, and right forearm and hand, with his wristwatch still on, were recovered a short distance from the camp. Huguenard’s partial remains were found next to the torn and collapsed tents, partially buried in a mound of twigs and dirt. A large male grizzly (tagged Bear 141) protecting the campsite was killed by park rangers during their attempt to retrieve the bodies. A second adolescent bear was also killed a short time later, when it charged the park rangers. An on-site necropsy of Bear 141 revealed human body parts such as fingers and limbs. The younger bear was consumed by other animals before it could be necropsied.[citation needed] In the 85-year history of Katmai National Park, this was the first known incident of a person being killed by a bear.