Ancestral worship is a religion based on the worship of dead ancestors. It is convergent and is widespread throughout the galaxy.
A family practicing this religion usually has a shrine dedicated to the ancestors of that family. Sometimes they single out particularly prominent, famous or successful ancestors on the shrine. Those ancestors might be worshiped and asked for guidance for generations to come.
Often, on special occasions, the ancestors are invited to join the living in celebration. Sometimes the ancestors are invited to occupy the bodies of some living members of the family, or they might be visited in trance by specialized shamans.
Whether the invited ancestors are actually the souls of the ancestors, some form of ghostly reflection of their personality, spirits that takes the form of the ancestors to gain divine energy, if the person being possessed is simply faking it, hypnotized by social expectations, or is insane, is usually up for debate in every individual instance of spirit worship.
Some ancestors get so strong, possibly because the families that worship them proliferate and spread to many planets that they become strong enough to have influence over entire planets or even multiple planets.
The stories told about some famous ancestors are spread throughout large parts of the galaxy.