The Hylund Hollow Pack of werewolves directly relates to Vesper's backstory since they are the same pack that killed his parents, bit him and turned him into a werewolf, and then did most of the task of raising him themselves. While one might argue that Vesper is almost feral as a character, the members of this pack are even more so, embracing their savage sides to a greater extent than even him.
The name Hylund Hollow is because the pack lives in a cave within a hollow in the northeastern part of the Hylund region, not far from Marth Village. They've been known to capture humanoids and drag them back to this lair as food or toys. They are at their most dangerous during any full moon events.