Death of the Old Gods

"Tell the king; the fair wrought house has fallen No shelter has Apollo, nor sacred laurel leaves The fountains are now silent; the voice is stilled. It is finished."

- The Oracle of Delphi to Emperor Theodosius

A common fantasy trope where the polytheistic pagan gods are slowly giving way to a single unified Christian god (or the nearest fictional approximation), although giving way to new polytheistic gods or no gods at all is not unheard of.

Normally their departure is a result of people no longer believing in them, although it's not unknown for them to simply lose interest in the affairs of mortals, or to die out for other reasons.

The fading gods and their worshipers are normally portrayed sympathetically, but there are normally underlying messages that their time is up and they should accept their fates.

Sometimes the result of a War in Heaven. Contrast Gotterdammerung, where the gods go out with a bang instead of a whisper. While the old gods will interact with the mortals on a common basis, the One True God will rarely make appearances despite his new found popularity (perhaps he's too busy keeping things running?). This is generally seen as an improvement compared to their predecessor however.

Comic Books

 * In Marvel Comics the pantheons of Earth were forced to stop intervening in humanity's progress (overtly anyway) 1000 years ago by The Celestials, beings who guide evolution. Most people—including most deities—do not know this, only the leaders of each pantheon.
 * Apparently, being a superhero doesn't count as "overtly intervening", given the examples of Thor and Hercules, and occasionally a few others.
 * In DC Comics, the Old Gods literally died in a huge war only to be replaced by New Gods; none of these were Earth gods, however.
 * Since the death of the New Gods in Final Crisis, and the foreshadowing that even newer gods will arise, the New Gods are now also old dead gods.

Fan Works

 * Justified in Thousand Shinji by Academia Nut where several deities from Warhammer 40,000 sacrificed themselves to create the newChaos gods so that the C'Tan can be defeated. However, in the sequel The Open Door, the newChaos gods’ learn that an alternate version of their predecessors exist elsewhere in the multiverse and have devised an elaborate Gambit Roulette to manipulate the inevitable war between the Old gods and the New gods for their own benefit.

Film

 * Beowulf laments that his people have abandoned "the Gods of might and power for a crying martyr" in the recent animated film.
 * The film version of The Egyptian draws parallels between Akhenaten's worship of the sun god Aten and later Judaeo-Christian monotheism. The end of the film implies that even though the priests of Amon-Re were able to quash to new religion, it would come again in a different form. It's very interesting to watch this film back-to-back with The Ten Commandments for this reason.
 * The miniseries Merlin has Merlin attempting to defeat the old gods (and put an end to magic itself) by spreading Christianity.

Literature
"''"What gods?" he muttered. "The nameless, forgotten ones. Who knows? They have gone back into the still waters of the lakes, the quiet hearts of the hills, the gulfs beyond the stars. Gods are no more stable than men."''"
 * In A Song of Ice and Fire, the Faith of the Seven, which resembles the Catholic Church, has largely replaced the Old Gods, who were worshiped by the original inhabitants of the continent. The only worshipers left are up north. Later in the series, the religion of R'hllor, a militant, monotheistic religion from the East, begins to take a foothold.
 * Winds of the Forelands series there is a monotheistic god, Ean, with steadily increasing worship and the favor of most of the aristocracy, but the religion of the old gods isn't out of the fight yet.
 * Juliet Marillier's Bridei Chronicles series has this, it's set in Scotland and England during their conversion from paganism to Catholicism.
 * Stephen R. Lawhead does this in his Pendragon Cycle of Arthurian stories. In his version, the old Celtic gods (Lleu of the Long Hand being the only one consistently named) give way to the Christian God, albeit gently. It's implied by the titular Taliesin of the first book that the Christian God was always there above the Celtic deities, but was unknown and thus not truly worshiped directly. With the coming of Christianity into this post-Roman Britain, there is no further need for the older forms of religion. The druids and other followers of the older faith after the introduction of Christianity are portrayed rather negatively, with the implication that they're only in it for the power (real, mystical or perceived).
 * Lawhead also does this in his Dragon King Trilogy, although here it's a bit different. Quentin, as an initiate at a temple of the old gods, seems mainly to learn less about the gods themselves and more about how the priests manipulate the people into thinking these gods are real, and reaping the benefits of the people's worship of said gods. The implication seems to be that if these older gods actually do exist, they are remarkably silent on all human affairs. Later on in the first book, a very familiar Christian-type God reveals himself to Quentin.
 * The original Dragonlance trilogy actually subverts this. After the Cataclysm, a world-shattering disaster visited on the world by the gods as punishment for a variety of sins, humanity decides to find itself a new pantheon, and the dwarves and elves seem to be less interested in worship generally speaking. It's later revealed, however, that the old gods were around all along; it was people's loss of faith in them that made them believe the old gods had departed. And, interestingly, it winds up being the goddess of evil who becomes active again in the world first.
 * Most of Thomas Burnett Swann's fantasy novels are about the fading of the old magic, mythology and gods, though it's implied that some have survived in hiding.
 * Neil Gaiman's American Gods is about a war between the Old Gods, who embody traditional myths and are running out of faith, and the New Gods, who embody things like television and the Internet and are rising in power but perhaps only as passing fads (like the railroad).
 * In Merry Gentry's world, the many of the Sidhe were worshiped as well-known Pagan gods, but lost their worshipers to Christianity. This marked the beginning of their decline in power. It is explicitly stated that Sidhe draw power from such worship, and are therefore forbidden to set themselves up as gods as part of the treaty with Jefferson. Furthermore, the older Sidhe have referred to the Elder Gods and Firblogs, which implies that there may have been even Older Old Gods, that the Sidhe didn't just Put on a Bus to Another Dimension, but actually Killed Off for Real.
 * In And Another Thing, Cthulhu applies for the job as a new world's god but he can't close the deal because nobody is currently worshiping him, since he's technically dead.
 * The Dresden Files notes that most of the old gods  have effectively gone into hibernation over the last few centuries. The Lord Almighty (as Harry calls the god of Christianity) is still very active in modern times.
 * Changes also reveals some of the Old Gods, specifically Mayincatec ones, to have actually been very powerful, very old vampires of the Red Court, called the Lords of Outer Night.
 * There is also a whole bunch of ancient deities so dangerous to the world that an Ancient Tradition of Venatori has been struggling for centuries to erase every trace of their presence, thus preventing mortals from believing in them and allowing them to exist. This is appropriately known as the "Oblivion War".
 * The end of Lord of Light has a Buddha analogue that replaces the Hindu gods.
 * Part of the backstory of Arcia Chronicles includes the Seven Lightbringers physically destroying all the Old Gods of Tarra. This returns to bite Tarra mightily in the ass nine thousand years later when the Lightbringers leave and a bunch of Cosmic Horrors show up to devour the now completely defenseless world.
 * In Poul Anderson's The Broken Sword, this has yet to happen to the Norse Gods, but the young hero met up with a satyr who recounts the fall of Olympus.
 * In Robert E. Howard's Conan the Barbarian story "The Shadows In The Moonlight", the sometimes animated statues were caused by a Physical God who appears gone now. (This is a polytheist-to-polytheist situation.)


 * The Mists of Avalon has this going on for most of the book, and being fought against tooth and nail by several main characters. Not that it has much effect in the long run.
 * It ends with
 * In the finale of Lawrence Watt-Evans' The Lords of Dûs series, it is revealed that.
 * The basis of the plot of Margaret Weis and Tracy Hickman's Dragonships series involves the old gods (a pantheon obviously inspired by, though not identical to, that of the Norse) getting their territory muscled in on by two sets of interlopers (the Gods of Raj and the Lord of the New Dawn, Aelon), and how that conflict spills over into the mortal world.
 * This is how the Books of Swords end. As humanity ceases to dream of the gods, they lose their power and fade from existence. As the last of them, Vulcan, dies, he senses the presence of some new power, or perhaps a returning old one, come to claim or reclaim the earth.

Live-Action TV

 * The new Battlestar Galactica Reimagined is all about this. The Cylons seek to replace the Greco-Roman gods of the colonies with their own vaguely Mormon God. A rare Sci-fi example.
 * An episode of Supernatural has two pagan gods eating humans around the Christmas season and one of them reflects on how Jesus is the big new thing.
 * "Hammer of the Gods" has a bunch of the "old gods" telling Sam and Dean to deal with Lucifer because they don't want the word to end when it's no longer theirs. By the end of the episode, most of them are dead. Like the earlier pagan gods, they seem to subsist on human flesh where once they subsisted on faith. Despite the fact that Ganesh and Kali are among their numbers, so apparently, India must've converted to Christianity at some point in the Supernatural-verse.
 * The show suggests that all non-Christian gods are just powerful people-eating monsters, who kill people themselves because they're no longer receiving sacrifices. Why they went down in the lore as mostly benevolent deities while all the other people-eating monsters show up as, well, people-eating monsters, is anyone's guess.
 * Xena: Warrior Princess plays fast and loose with this. Early on, . Later,.
 * She also ran into a Greek Expy Abraham before any of that (and played a big part in his NOT sacrificing the Isaac Expy).
 * The Star Trek episode "Who Mourns For Adonais" has the Enterprise meeting Apollo, the last of the Greek gods (who were actually Sufficiently Advanced Aliens). Kirk pretty much tells him to stuff it, and then gets schizophrenic about if humanity has Outgrown Such Silly Superstitions as religion in general, or just moved on to Christianity.
 * More or less the plot to Stargate SG-1 as over 10 seasons the Old Gods are all killed off. Aside from the fact that they weren't gods, just Sufficiently Advanced Aliens.
 * The BBC version of the Arthurian legends, Merlin, can't seem to be able to make it's mind up about the 'Old Religion' (the pagan religion that existed before Christianity and, despite the show's claims, did not involve priestesses using pygmy hydra to control peoples' minds): after three years of portraying these old ways as almost uniformly evil, Series 4 begins with the royal court of Camelot celebrating the feast of Samhain, briefly mentions Ostara and ends as they prepare to celebrate Beltane. All of which are fire festivals celebrated by the aforementioned 'Old Religion'. To confuse matters further, King Arthur (in this same series) "swears to God" at least twice.

Mythology and Legend

 * Most modern re-tellings of the Arthurian legends have this going on at least in the background.

Poetry

 * The main idea behind John Milton's poem "On the Morning of Christ's Nativity."

Tabletop Games

 * In Pendragon the Christian religion is replacing the old nature gods of Britain.
 * Averted in Scion, where All Myths Are True and each newly risen pantheon gets the divine equivalent of a fruit basket from the old ones. The reality of the Abrahamic religions are left up to the Storyteller, but they don't seem to have done any damage to the old gods (most of which don't really care about having worshipers, since Fate loves to screw with them via those links).

Video Games

 * In Dragon Age the Old Gods of the Tevinter Imperium (AKA Dragons) were struck down by the Maker. Most of the world now worships the Maker and his prophet Andraste, and the Old Gods slumber beneath the Earth until they're awoken, one at a time, to lead the corrupted darkspawn in a Blight.
 * The elves' gods were tricked by a being known as Fen'Harel that trapped both them and their mysterious enemies beyond the reach of their followers, presumably keeping them from helping the Elves when their ancient empire was destroyed.
 * God of War shows why Greek Gods don't exist anymore:.
 * In Breath of Fire II, the old animist dragon gods are being forgotten in favor of a new I-Can't-Believe-It's-Not-Catholicism! monotheistic religion.
 * In the Shin Megami Tensei series, YHVH is the Big Bad, who intentionally tries to destroy all other gods so only he will be worshiped. However, YHVH is (according to Word of God) not the real cause behind this (his evil is a symptom, not the disease).
 * Though there are Gods that serve YHVH willingly and aid him.
 * In Arcanum: Of Steamworks and Magick Obscura, the pantheons of the old gods have all been forgotten, except for a few like the Cult of Gestianna (because they have annual orgies), and the pacifistic Order of Halcyon. The greater populace is being swept up by the Panarii religion; a deliberate Christianity likeness centered around the teachings of a Jesus-figure elf called Nasrudin. Ironically  where as the Old Gods are still alive and able to give blessings (stat-boosts) to those who worship at their altars. There's even a side-quest involving a complex ritual of offerings that let the protagonist become a god themselves.
 * Happens in Touhou, magic giving way to rationalism and thus the old gods give way to a whole new godless world. Suwako was prepared to accept it, but Kanako decided to fight this fate. On the other end of spectrum, the oni also accept that they have no place in the modern world, and retreated underground. Except Suika.
 * Castlevania: Lords of Shadow mentions this, that all the old physical gods and mythical beasts are slowly dissapearing from the world.

Web Comics

 * The Gods of Arr-Kelaan has a very unusual example. The old gods are gradually forced away from earth by the expansion of the universe but  They didn't so much remove the old gods as outlast them, most of the angels were originally one of the old gods. The planet of Arr-Kelaan qualifies too, but just barely. The Traveller gods do kick out the old gods, but the old gods are immigrants from Earth's universe who've barely held established religions longer than the Travellers.