The Capricorn Killer was originally an ordinary office worker. One night outside a bar he was approached by a woman who bit his neck and began to drink his blood. She left him when she heard a noise nearby.
He discovered that he was changed. He had a craving for blood. He had no reflection, though he could appear in photographs. He avoided being out in the daylight, and spent his nights in bars.
One night he was provoked by another man and killed him, drinking his blood. He continued to kill, and was named the "Capricorn Killer" by the media, supposedly because of his goatee.
He was finally killed when the Fourth Doctor plunged a walking stick through his heart. (PROSE: I Was a Monster!!!)