
In the movie, they were created by a character named Mean Mr. Mustard (played by Frankie Howerd) who invented them to be his evil robot henchmen, called the Computerettes.
So far about their background in this movie.
The movie itself was released in June, 1978, two months prior before Battlestar Galactica's premiere. To save some costs, it makes sense the BSG production crew used the molds for the already existing Computerette heads to have them altered to become the IL-Series Cylon head we all know today.
Again, it's perfect example of prop reuse at its very best.
If you take a close look at the screencaps, you'll realize how close they look even in their pre-BSG appearance:








