The Praetor Lupus is a secret organization made up of werewolves. It literally means "Wolf Guardians," based on the Praetorians, an elite Roman military force. The Shadowhunters are aware of the Praetor's existence and do not interfere with their work.
Guardians are able to observe and research their charges extensively beforehand; they have the means and resources to set up favorable conditions on short notice. Once Praetors are given their assignment, they are bound by oath to follow through and are not allowed to choose or withdraw from their missions.
Downworlders that the Praetor Lupus has helped, or tried to, at one point (listed in order of when they were given aid):