Although wolves have always been native to the Yellowstone area they have been the subject of extermination attempts by misguided humans in the past. Various diseases that can kill canids were released into the Yellowstone area eco-system that decades later still affect entire litters of pups.
From 1995 to 1997, 41 wild wolves from Canada and northwest Montana were released in Yellowstone National Park. The Lamar Valley was the original location for the release of Grey Wolves to the Yellowstone National Park to repopulate wolves that originally were native to Yellowstone. In general, wolf numbers have fluctuated between 83 and 108 wolves from 2009 to 2016. By comparison the state of Wisconsin has roughly 900 wolves.
Hence, the Lamar Valley provides for some of the best wolf viewing in the United States. However, you must be an early riser. Most wolf watchers arrive as the sun rises and the hot sun drives most of the predators out of the open into the cool forests by 8 am. On this day there is a carcass of a Bison, that died of natural causes, near the middle of the Lamar Valley. There were four wolves from the Junction Pack at the carcass, three black and one grey.