GENIUS (from Lat. genere, gignere), a term which originally meant, in Roman mythology, a generative and protecting spirit, who has no exact parallel in Greek religion, and at least in his earlier aspect is of purely Italian origin as one of the deities of family or household. Every man has his genius, who is not his creator, but only comes into being with him and is allotted to him at his birth. As a creative principle the genius is restricted to man, his place being taken by a Juno (cp. Juno Lucina, the goddess of childbirth) in the case of women. The male and female spirit may thus be distinguished respectively as the protector of generation and of parturition (tutela generandi, pariendi), although the female appears less prominent. It is the genius of the paterfamilias that keeps the marriage bed, named after him lectus genialis and dedicated to him, under his special protection. The genius of a man, as his higher intellectual self, accompanies him from the cradle to the grave. In many ways he exercises a decisive influence on the man's character and mode of life (Horace, Epistles, ii. 2. 187). The responsibility for happiness or unhappiness, good or bad fortune, lay with the genius; but this does not suppose the existence of two genii for man, the one good and the other bad , an idea borrowed from the Greek philosophers. The Roman genius, representing man's natural optimism, always endeavoured to guide him to happiness; that man was intended to enjoy life is shown by the fact that the Roman spoke of indulging or cheating his genius of his due according as he enjoyed himself or failed to do so, when he had the opportunity. A man's birthday was naturally a suitable occasion for honouring his genius, and on that occasion offerings of incense, wine, garlands, and cakes were made (Tibullus ii. 2; Ovid, Tristia, iii. 13. 18). As the representative of a man's higher self and participating in a divine nature, the genius could be sworn by, and a person could take an oath by his own or some one else's genius. When under Greek influence the Roman idea of the gods became more and more anthropomorphized, a genius was assigned to them, not however as a distinct personality. Thus we hear of the genius of Jupiter (Jovis Genio, C.I.L. i. 603), Mars, Juno, Pluto, Priapus. In a more extended sense the genius is also the generator and preserver of human society, as manifested in the family, corporate unions, the city, and the state generally. Thus, the genius publicus Populi Romani - probably distinct from the genius Urbis Romae, to whom an old shield on the Capitol was dedicated, with an inscription expressing doubt as to the sex (Genio ... sive mas sive femina) - stood in the forum near the temple of Concord, in the form of a bearded man, crowned with a diadem, and carrying a cornu copiae and sceptre. It frequently appears on the coins of Trajan and Hadrian. Sacrifice, not confined to bloodless offerings like those of the genius of the house, was offered to him annually on the 8th of October. There were genii of cities, colonies, and even of provinces; of artists, business people and craftsmen; of cooks, gladiators, standard-bearers, a legion, a century, and of the army generally (genius sanctus castrorum peregrinorum totiusque exercitus). In imperial times the genius of Augustus and of the reigning emperor, as part of the sacra of the imperial family, were publicly worshipped. It was a common practice (often compulsory) to swear by the genius of the emperor, and any one who swore falsely was flogged. Localities also, such as theatres, baths, stables, streets, and markets, had their own genius. The word thus gradually lost its original meaning; the nameless local genii became an expression for the universality of the divinum numen and were sometimes identified with the higher gods. The local genius was usually represented by a snake, the symbol of the fruitfulness of the earth and of perpetual youth. Hence snakes were usually kept in houses (Virgil, Aen. v. 95; Persius i. 113), their death in which was considered a bad omen. The personal genius usually appeared as a handsome youth in a toga, with head sometimes veiled and sometimes bare, carrying a drinking cup and cornu copiae, frequently in the position of one offering sacrifice.
See W.H. Roscher, Lexikon der Mythologie, and article by J.A. Hild in Daremberg and Saglio, Dictionnaire des antiquités, where full references to ancient and modern authorities are given; L. Preller, Römische Mythologie, 3rd ed., by H. Jordan; G. Wissowa, Religion und Kultur der Römer.
Apart from the Latin use of the term, the plural "genii" (with a singular "genie") is used in English, as equivalent to the Arabic jinn, for a class of spirits, good or bad, such as are described, for instance, in The Arabian Nights. But "genius" itself has become the regular English word for the highest conceivable form of original ability, something altogether extraordinary and beyond even supreme educational prowess, and differing, in kind apparently, from "talent," which is usually distinguished as marked intellectual capacity short only of the inexplicable and unique endowment to which the term "genius" is confined. The attempt, however, to define either quality, or to discriminate accurately between them, has given rise to continual controversy, and there is no agreement as to the nature of either; and the commonly quoted definitions of genius - such as Carlyle's "transcendant capacity of taking trouble, first of all,"  in which the last three words are usually forgotten - are either admittedly incomplete or are of the nature of epigrams. Nor can it be said that any substantial light has been thrown on the matter by the modern physiological school, Lombroso and others, who regard the eccentricity of genius as its prime factor, and study it as a form of mental derangement. The error here is partly in ignoring the history of the word, and partly in misrepresenting the nature of the fact. There are many cases, no doubt, in which persons really insane, of one type or another, or with a history of physical degeneration or epilepsy, have shown remarkable originality, which may be described as genius, but there are at least just as many in whom no such physical abnormality can be observed. The word "genius" itself however has only gradually been used in English to express the degree of original greatness which is beyond ordinary powers of explanation, i.e. far beyond the capacity of the normal human being in creative work; and it is a convenient term (like Nietzsche's "superman") for application to those rare individuals who in the course of evolution reveal from time to time the heights to which humanity may develop, in literature, art, science, or administrative life. The English usage was originally derived, naturally enough, from the Roman ideas contained in the term (with the analogy of the Greek ), and in the 16th and 17th centuries we find it equivalent simply to "distinctive character or spirit," a meaning still commonly given to the word. The more modern sense is not even mentioned in Johnson's Dictionary, and represents an 18th-century development, primarily due to the influence of German writers; the meaning of "distinctive natural capacity or endowment" had gradually been applied specially to creative minds such as those of poets and artists, by contrast with those whose mental ability was due to the results of education and study, and the antithesis has extended since, through constant discussions over the attempt to differentiate between the real nature of genius and that of "talent," until we now speak of the exceptional person not merely as having genius but as "a genius." This phraseology appears to indicate some reversion to the original Roman usage, and the identification of the great man with a generative spirit.
Modern theories on the nature of "genius" should be studied with considerable detachment, but there is much that is interesting and thought-provoking in such works as J.F. Nisbet's Insanity of Genius (1891), Sir Francis Galton's Hereditary Genius (new ed., 1892), and C. Lombroso's Man of Genius (Eng. trans., 1891).
 Frederick the Great, iv. iii. 1407.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)