Actually there is an interesting story behind all this.
https://www.bibleodyssey.org/en/passages/related-articles/666-in-popular-culture-and-history
https://theconversation.com/no-the-covid-19-vaccine-is-not-linked-to-the-mark-of-the-beast-but-a-first-century-roman-tyrant-probably-is-158288 (explains a little easier)
In short: Many biblical scholars maintain that the first beast is a symbolic representation of first-century Roman emperors. In this reading, each head would represent one emperor. While there is some debate in scholarship on which specific emperors the author of Revelation is alluding to, there is fairly widespread agreement that Emperor Nero is one of them.
Satan was Gods favorite angel, the angel of righteousness but Satan betrayed God.
His depiction as a Goat is actually from Paganism, where the Horns symbolize a crown of power. In older symbolism he wasn't depicted with horns or as a goat.
The sign of the horns which is used by metalheads (R.I.P. Ronnie James DIO) actually comes from an old Italian superstition of giving someone the evil eye (or in reverse, avoiding the evil eye), and is believed to even be older than this (dating back to India where it symbolizes a rejection of any negative spirit or energy), Ronnie adapted this symbolism as an alternative to Ozzy Osborn's peace sign, during the begin times of Black Sabbath.
I'm merely using this name because of my love for metal music and because I fear no evil (Psalm 23:4). Also because I'm happily insane🤘🏼🤘🏼