Four Horsemen of the Apocalypse
The things the Horseman represent in pestilence, famine and war are like forces of nature and are states that humans experience all the time. So it isn't as though when Lucifer comes on the scene he brings these monsters with him that are unleashed that we haven't been experiencing the effects of throughout history. It's more that he gathers them to him.
– Sera Gamble, Supernatural: The Official Companion Season 5
http://www.supernaturalwiki.com/index.php?title=Four_Horsemen_of_the_Apocalypse
