From Wikipedia
During the rise of Christianity, a depiction of Satan as a horned and hoofed goat-like monster holding a trident, adopted from Greek Pan, became popular. By adopting the image of the Horned God and transforming it into an image of the Devil, the Christian church implied that paganism was evil. The similarity does not extend beyond the image, of course; while Judeo-Christian Satan is described as a fallen angel and essentially evil, the pagan Horned God is believed to be a force of nature, neither entirely benevolent nor entirely malevolent: In his role as Father, he is said to give life, but in his role as Hunter, he is also said to take life. Positive aspects of the Horned God are re-attributed to Satan by the Church of Satan and similar branches of modern Satanism.