Many Bible translators misinterpreted the ancient Hebrew text - even Rabbis and Jerome
Moses with horns, by Michaelangelo
Due to a statement towards the end of the book of Exodus (at 34:29-35), in which Moses is depicted as having been disfigured due to his direct encounter with God, various traditions grew up as to what the disfigurement was. Jonathan Kirsch, in his book Moses: A Life, thought that, since Moses subsequently had to wear a veil to hide it, the disfigurement was a sort of "divine radiation burn".
There is one longstanding early tradition that Moses grew horns, derived from a mistranslation of the Hebrew phrase "karnu panav" ???? ????. The root ??? may be read as either "horn" or "ray", as in "ray of light". "Panav" ???? translates as "his face". If interpreted correctly those two words form an expression which means that he was enlightened, and many rabbinical studies explain that the knowledge that was revealed to him made his face metaphorically shine with enlightenment, and not that it suddenly sported a pair of horns. The Septuagint properly translates the Hebrew word ??? as ??????????, 'was glorified', but Jerome translated it as cornuta, 'horned', and it was the latter image that became the more popular. This tradition survived from the first centuries AD well into the Renaissance. Many artists, including Michelangelo in a famed sculpture, depicted Moses with horns.