There was not much place for the Evil One in the Old Testament, since God himself was portrayed as booth good and evil, merciful and vengeful. It is only in the New Testament that he becomes a real character, albeit still a vague presence.
Gradually, over the centuries, he started collecting physical characteristics, to become the horned figure we see in horror movies, with influences from other religions and popular folk tales. No depiction of him even exists before the sixth century. And in popular beliefs, strongly influenced by the church, he became a real presence in people's everyday life over the centuries, and now gradually being reduced back to the fantasy figure he always was to the realm of fiction and movies.
It is fascinating to read how he has been used over the centuries, how he instilled fears in uneducated populations. In sermons some hundred years ago, he was still often mentioned in Europe. I think he has even completely disappeared from all sermons these days in Europe, with the exception maybe of some maverick extremists.
Everything he every embodied, has now been reduced to our human psyche (the internal evil) and to chance happenings (earthquakes, floods). There seems to be no need anymore to blame a distinct person to create and organise all that's unwelcome in society.