Vampires on Golarion share a common ancestor, the strigoi, who came from the Plane of Shadow for reasons lost to history. The Whispering Way believes a necromancer opened a portal to bring strigoi to Golarion. These original strigoi no longer exist, having either died out—all evolved into one of the current varieties of vampire—or returned to their home plane.
Nosferatu evolved first, driven to rage by their hunger and decay. Some of these adopted the traits of their human prey, pretending to nobility and youthful exuberance, becoming the moroi. Those that rebelled against drinking the filthy blood of lesser beings nearly starved out, but eventually evolved into the vetala. Strigoi who hibernated for hundreds or thousands of years wake up, driven by their desires, and are now jiang-shi.