It Came From Outer Space (1953)

While looking through his telescope one night, John Putnam (Richard Carlson) sees what at first appears to be a meteor shower -- but it is actually a crash-landing alien spaceship! After investigating the crater from the impact, John informs the town sheriff (Charles Drake), and receives nothing but ridicule. Even his fiancée, Ellen (Barbara Rush), is skeptical. All that changes when the townsfolk start disappearing, and are replaced by eerie alien duplicates.