Many cultures and religions contain some concept of demonic possession, but the details vary considerably. The oldest references to demonic possession are from the Sumerians, who believed that all diseases of the body and mind were caused by "sickness demons" called gidim or gid-dim. The priests who practised exorcisms in these nations were called ashipu (sorcerer) as opposed to an asu (physician) who applied bandages and salves. Many cuneiform clay tablets contain prayers to certain gods asking for protection from demons, while others ask the gods to expel the demons that have invaded their bodies.
Shamanic cultures also believe in demon possession and shamans perform exorcisms. In these cultures, diseases are often attributed to the presence of a vengeful spirit (or loosely termed demon) in the body of the patient. These spirits are more often the spectres of animals or people wronged by the bearer, the exorcism rites usually consisting of respectful offerings or sacrificial offerings.
Christianity holds that possession derives from the Devil, i.e. Satan, or one of his lesser demons. In many Christian belief systems, Satan and his demons are actually fallen angels.
The video below expounds on 5 knows cases of possible demonic possession, some were most likely sad cases based on medical conditions, others are still unexplained. Regardless most of them are very creepy.
Do you believe in the supernatural?