Deus Ex Machina

The Ancient Greeks were famous for theater. One of the more famous tragedy writers, Euripides, had a knack for writing his characters into hopeless situations. Then one of the gods would sweep down from Mount Olympus and save the day. On stage, an actor playing the god would be lowered into the scene by a crane. This plot device came to be known by the Latin "deus ex machina"--literally, "god from a machine".

If you look, you can still find a deus ex machina or two in modern storylines. The term still applies when it is a person, thing, or nature that saves the day. When Fawkes the phoenix flew in to save Harry Potter in The Chamber of Secrets, that would be a deus ex machina. Another example is in War of the Worlds when the aliens that have been killing everybody die from a common virus.