When Yellowstone was established in 1872 as the world’s first national park, officials set out to kill off the predators. By 1926, all the wolves were gone. But removing the wolves threw the ecosystem out of whack. “It was the mindset at that time—predators are bad,” says Doug Smith, director of the Yellowstone Wolf Restoration Project, who led the effort to restore the animals in 1995. Now there’s a stable population of 99 wolves, in ten packs. Clashes with cattle remain an issue, and hunters decry the smaller elk herds, but Smith says their huge numbers had left no vegetation for other animals to eat. Meanwhile, Yellowstone has become the best place in the world to view wild wolves, bringing in $35 million per year for the surrounding communities. “Many have called it the greatest wildlife conservation success story of the 20th century,” Smith says.