Demon or demoniac or demonic or demonology.
In Greek daimon was a word of rather fluid definition. In Homer the Olympians are referred to as either gods (theoi) or daimones ("divine powers"). In later literature the daimones became intermediate beings between gods and men or often the spirits of the dead came to be called daimones, especially among the Romans. Daimon could also denote that particular spirit granted to each mortal at his birth to watch over its charge. This corresponds to the Roman Genius, a vital force behind each individual, originally associated with male fertility and particularly with the male head of a household. Later it became a tutelary spirit assigned to guide and shape each person's life. With the triumph of Christianity, all pagan deities were suspect, and daimon, viewed solely as a power sprung from the devil, became our demon (any evil or satanic spirit). As an adjective demoniac or demonic suggests possession by an evil spirit and can mean simply fiendish. As a noun demoniac refers to one who is or seems possessed by a demon. Demonology is the study of evil spirits. As for genius, it has come to denote a remarkable, innate, intellectual or creative ability, or a person possessed of such ability. Through French we have the word genie, which had served as a translation of Jinni, spirits (as in the Arabian Nights) which have the power to assume human or animal form and supernaturally influence human life.