When "Supernatural" premiered on what was then The WB network in 2005, creator Eric Kripke mapped out a three-season plan for the show, which he later expanded to five. Now, Sam and Dean Winchester (Jared Padalecki, Jensen Ackles) end their ghost-busting road trip, as the longest-running live-action American fantasy series in TV history closes a 15-season run. Whatever happens in this series finale, we can borrow an epitaph from another cult hit, "Buffy the Vampire Slayer," for a final word on Sam and Dean: "They saved the world a lot."