Four Horsemen of the Apocalypse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun plural In the book of Revelation, four horsemen that personify pestilence, war, famine, and death, sent as harbingers of the end of the world.

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• proper noun biblical Four beings in Revelation 6:1–8 that bring about the Apocalypse, each riding a different-colored horse representing a different aspect of the Apocalypse.
• proper noun idiomatic Harbingers of doom; several signs which combine to imply the imminence of literal or figurative destruction.