When the action hit “Cloverfield” thrilled audiences in 2008, few in theaters could have guessed that they were, at least in part, under the creative stewardship of Steven Spielberg. That’s because Mr. Spielberg has no credit on the production. But that didn’t stop him from giving the movie’s director, Matt Reeves, and its producer, J. J. Abrams, advice on how to improve the film.

“He had this idea about the ending,” said Mr. Reeves, who, with Mr. Abrams, had sent Mr. Spielberg a cut during postproduction with the hope that he would give them creative notes. That version showed the giant monster that wreaks havoc on New York being last seen on the loose, at war with fighter jets. “The movie was meant to be open ended, but something was missing.”

Mr. Spielberg suggested the inclusion of air-raid sirens to give the impression of a countdown. “It prepared you so that even though the ending was still inconclusive, it wasn’t letting you fall off a cliff,” Mr. Reeves said. “It helped the movie a lot.”

Mr. Spielberg, 66, is considered the most influential director of our time, thanks to the impact of the 27 features that he has directed (which now include “Lincoln”). And then there are the more than 175 films that he, in one form or another, has been ultimately responsible for, mostly through his production company, Amblin, and his studio, DreamWorks.