When a large magnetic anomaly is discovered on the moon, humanity uncovers an ancient observer of life in the solar system that has been guiding human development for millennia.

Was written alongside the film: 2001: A Space Odyssey

For some reason or another, most species of aliens in the universe look like humans. Can be due to budget constraints, a lack of imagination, or the analogy nature of the story.

Sometimes justified in-story by common descent from Forerunner Race or Panspermia.