Institution (History Of The Teaser Trailer)

An early example of the teaser trailer was for 'Superman - The Movie' (1978) directed by Richard Donner:

The trailer was made to re-invigorate interest in the film as it was already nearly a year late. This marketing move was successful and the film was a massive success, being nominated for three oscars.
Another example of an early teaser trailer was for 'Batman' (1989) directed by Tim Burton:

The reason Warner Brothers created this teaser trailer was, again, for a specific reason. It was an emergency marketing move that successfully convinced angered comic book fans that the film would stay true to and respect the source material.
After these teaser trailers successfully aided in making the films massive successes, Hollywood started to create teaser trailers for most of their films, releasing the trailers long before the film's were due to be released, sometimes even before the films had finished being made.