In Judeo-Christian theology, for example, the Book of Enoch (an apochryphal book of the Bible whose complete version has only recently been discovered as a part of the Dead Sea Scrolls) describes the fall of the Watchers and the demons who might be the Fallen Angels (Watchers) themselves, or the offspring of the union of the Watchers and mankind. These creatures are said to wander the world in the form of evil spirits -- endlessly yearning for food though they have no mouths to eat -- endlessly thirsty though they cannot drink. Endlessly seeking these things from the living, the evil spirits seek to possess weak-willed men and women to dispossess their spirits and to take over their bodies so as to partake of food and drink. On the positive side, in Judaic tradition, the good but obviously thirsty spirit of Elijah, the prophet, visits every Jewish house during Passover to sample the wine. At every Passover Seder, a Jewish family will put out an extra glass of wine meant to satisfy the hungry ghost Elijah.
In the Roman religion, hungry ghosts of a family's ancestors figured in the festival of Lemuria; it was the duty of the pater familias to appease the larvæ of his ancestors with an offering of beans. The Balkan tradition of the vampire is another malevolent sort of undead revenant, a corpse supernaturally animated which seeks to feed on the blood of the living.
In Hindu tradition, much as described in the Book of Enoch, hungry ghosts are spirit-beings driven by the passionate objects of their desire. This concept was adopted by Buddhism.
Hungry ghosts also appear in Chinese ancestor worship. Some Chinese believe that the ghosts of their ancestors return to their houses at a certain time of the year, hungry and ready to eat. A festival is held to honor the hungry ancestor ghosts and food and drink is put out to satisfy their needs.
When Buddhism entered China, it encountered stiff opposition from the Confucian adherents to ancestor worship. Under these pressures, ancestor worship was combined with the Hindu/Buddhist concept of the hungry ghost. Eventually, the Hungry Ghost Festival became an important part of Chinese Buddhist life.