Damien is the spawn of Satan. His parents have no idea that their own baby was murdered after its birth and he was substituted. (He was born to a she-wolf.) Anyway, when his adoptive mother catches on that something is amiss, he kills her. When his father, an Ambassador, played by Gregory Peck, finds out the truth, he decides to kill him on a church altar. But, he is shot by the local police before he can complete the task.
In The Omen II, Damien is a grown man who becomes Senator with his eyes on the White house. Very scary - - the thought, not the movie.