In Roman religion, the genius (ˈɡɛnɪ.ʊs; plural geniī) is the individual instance of a general divine nature that is present in every individual person, place, or thing. Much like a guardian angel, the genius would follow each man from the hour of his birth until the day he died. For women, it was the Juno spirit that would accompany each of them.
Each individual place had a genius (genius loci) and so did powerful objects, such as volcanoes. The concept extended to some specifics: the genius of the theatre, of vineyards, and of festivals, which made performances successful, grapes grow, and celebrations succeed, respectively. It was extremely important in the Roman mind to propitiate the appropriate genii for the major undertakings and events of their lives.
Thus man, following the dictates of his heart, venerated something higher and more divine than he could find in his own limited individuality, and brought to "this great unknown of himself" offerings as a god; thus compensating by veneration for the indistinct knowledge of his divine origin.
The Christian theologian Augustine equated the Christian soul with the Roman genius, citing Varro as attributing the rational powers and abilities of every human being to their genius.
Although the term genius might apply to any divinity whatsoever, most of the higher-level and state genii had their own well-established names. Genius applied most often to individual places or people not generally known; that is, to the smallest units of society and settlements, families and their homes. Houses, doors, gates, streets, districts, tribes, each one had its own genius. The supreme hierarchy of the Roman gods, like that of the Greeks, was modelled after a human family. It featured a father, Jupiter, who was also the supreme divine unity, and a mother, Juno, queen of the gods. These supreme unities were subdivided into genii for each individual family; hence, the genius of each female, representing the female reproductive power, was a Juno. The male power was a Jupiter.