Source: Blood of the Night, pg(s). 4-5
Strigoi are the ancestors of modern vampires. They were originally from the Plane of Shadow, but somehow made their way to Golarion. The Whispering Way counts among its secrets the belief that a necromancer summoned them via a portal. There are no known strigoi existing today, but they have evolved into four types of modern vampire.
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.