One of Yellowstone National Park’s most important predators completely disappeared in the early part of the 20th Century. By the 1920s, the last wolf pack in Yellowstone was killed, in an effort by the U.S. government to "tame the wilderness". The park was missing a keystone species and it affected the balance of the entire ecosystem. Thanks to the Endangered Species Act passed in the 1970's, the National Park Service began planning the return of grey wolves to Yellowstone. In January 1996, fourteen gray wolves were captured in Canada and relocated to Yellowstone’s Lamar Valley. The wolf population grew quickly, and their impact has been significant; wolves have affected the entire Yellowstone ecosystem. While the federal government funded the original restoration and monitoring of wolves, funding was cut and Yellowstone Forever, established in 1996, stepped in to raise funds to continue wolf research and monitoring in the park. Yellowstone has the most recognizable wolf conservation program in the world and is conducting cutting-edge research. As of 2015 an estimated 528 wolves resided in the Greater Yellowstone Ecosystem and 94 wolves in eight packs currently live in the park.