Strigoi is based on the ancient Greek term strix for screech owl, which also came to mean demon or witch. Before the popularization of vampire, it was the name most frequently used for the kind of undead vampire that periodically returns to its grave.
Another use of the term is a living person with certain supernatural powers including a form of psychic vampirism that is destined to return to become an undead strigoi. Often, this a person born with a caul or with a small tail at the base of the spine.
Most often, as is typical of the undead in eastern and central European folk belief in general, an undead strigoi would first prey on his or her family. In some Romanian tales, the undead strigoi was first invisible and raided its former house hold by creating chaos like a poltergeist and obtained nourishment by eating food in the family larder.
The strigoi might also come to the household appearing just as it did when alive, engage in conversation with the living members, and go about performing normal, routine chores as if its death had not occurred, but more often the report of such a visit involved deaths of members of the household or farm animals belonging to the household. (In the case of vampires who died unmarried, there are tales where they came to the homes of their former lovers seeking to entice them.)
As is the case in Greece for the vrykolakas, it was commonly believed in Romania that the undead strigoi only had to be back in their graves on each Saturday.
There are also tales and an anecdotes collected by Romanian folklorists in which the undead strigoi can take the form of an animal such as a cat, a dog, or a sheep. And there are tales where male strigoi take the form of handsome young men who come into villages at night to mingle with the young people at social gatherings. In some of these tales, only one girl becomes the victim. In others, one girl escapes while the rest become the victims.
Some contemporary Romanian folklorists deny that Romanians ever associated the undead with blood-drinking. But there is plenty of evidence to the contrary in articles and other literature based on tales and anecdotes collected from common people by Romanian scholars prior to the end of World War II. When details of the precise manner in which the undead strigoi drinks his blood are given, it is said that he drinks it directly from the heart. Sometimes it was said that the strigoi fed upon the heart itself. Yet in other accounts the undead strigoi devours its victim’s soul which it sucks up through the mouth or nose of the victim.
The strigoi was also believed capable of causing droughts or causing so much rain those floods resulted.
According to Adrien Cremene’s book, Mythologie du Vampire en Roumanie, it was sometimes said that an undead strigoi had two hearts. The second, extra heart is the one where his vitality resides. It is this heart which spurts out blood when a stake is driven through it. The same belief is found in Slovakia.
The ultimate ways of destroying an undead strigoi following exhumation include
It was believed that if a strigo was not destroyed within seven years after burial, then on the seventh year it would no longer have to dwell in its own grave and could pass as a normal mortal human. According to one source, the strigoi also then loses his need to prey upon humans and, eventually, even animals. Like the Serbian vampire at such a stage, it would then depart to another region where it could not be recognized, marry, and have children But each week, from Friday night to Sunday morning, such a strigoi would either have to rest in a grave in a nearby cemetary or meet with the local strigoi for supernatural social activities. The children of such a vampire were all "living vampires", destined to become undead themselves.