Barnabas was originally, indeed, a villain. Supposedly, it was to be a thirteen-or-so-week arc. Barnabas was to bring terror and Dr. Julia (originally "Julian" - a man) Hoffman would find out what he was and the battle was on. At the climax, both characters would die and on to the next monster. Jonathan Frid, ready to move to the west coast to teach acting as a university, was told by his agent that the gig would be three months and giving him extra cash, so he delayed his move for the ca-ching. But the ratings kept skyrocketing and the original plot was altered to extend it and the rest, as they say, is history.
Gerard