The Pack is a group of therianthropes living inside Sanctuary. They consider themselves “the sane ones” because they can keep their human minds when they transform. Their alpha (leader) is Bastet (Anna Wu), who has the form of a panther.
Before the Pack, Sanctuary was a place where might made right, and people with less powerful forms got pushed around. The Pack was created by Bastet and Lyonnesse, who as a panther and a lion, were powerful enough to make anyone think twice. Their goal was to establish a place where people didn’t have to worry about being attacked, and where they could live as civilized a life as possible.
Most of the other theris in Sanctuary were living in small gangs, though some lived (or tried to live) on their own. The Pack had to defend themselves against these gangs until the Wall was built to separate the theris interested having some law and order from the ferals.
The Pack members joined bit by bit. Some joined for basic survival, others to escape the gang-packs they been roped into, or to avoid being dragged into one in the first place.
The Pack refers to all theri groups as packs, each one has a proper name. They call themselves “Bastet's Pack”, and other packs also get called after the leader’s name, if they know it. If they don’t, they call them things like “the pack with the hyena”, or “the pack from the canyon”.