History Main / TheConstant

* ''Franchise/{{Nasuverse}}'': The series actually [[JustifiedTrope justifies]] this with the Quantum Time-Lock system put in place by [[DeusEstMachina The World]]. As a limited amount of "water" exists to sustain so many worlds without the universe effectively overloading on the sheer weight of possibilities, Quantum Time-Locks happen every once a hundred years or so to ensure that Constants exist present in all other timelines (e.g. Camelot falling). [[CuttingOffTheBranches Any other timelines that have anything different happen are purged altogether in a process known as 'pruning']]. However, while there exists several Quantum Time-Locks across human history, the ''median'' of which these Time-Locks happen can be extraordinarily variant to a variety of possibilities; it's just that the Quantum Time-Locks are a means of ensuring the most prosperous timelines for humanity survive, and any that have grown past the point of being able to be changed are as a result pruned.

[[quoteright:253:[[VideoGame/StarOceanTillTheEndOfTime https://static.tvtropes.org/pmwiki/pub/images/the_constant_star_ocean_tetot.png]]]]
[[caption-width-right:253:[[Film/PlanetOfTheApes1968 You maniacs!]] You built it up!]]

[[quoteright:253:[[VideoGame/StarOceanTillTheEndOfTime https://static.tvtropes.org/pmwiki/pub/images/the-constant_star-ocean-tetot2_4298.png]]]]

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* ''Franchise/{{Nasuverse}}'': The series actually [[JustifiedTrope justifies]] this with the Quantum Time-Lock system put in place by [[DeusEstMachina The World]]. As a limited amount of "water" exists to sustain so many worlds without the universe effectively overloading on the sheer weight of possibilities, Quantum Time-Locks happen every once a hundred years or so to ensure that Constants exist present in all other timelines (e.g. Camelot falling). [[CuttingOffTheBranches Any other timelines that have anything different happen are purged altogether in a process known as 'pruning']]. However, while there exists several Quantum Time-Locks across human history, the ''median'' of which these Time-Locks happen can be extraordinarily variant to a variety of possibilities; it's just that the Quantum Time-Locks are a means of ensuring the most prosperous timelines for humanity survive, and any that have grown past the point of being able to be changed are as a result pruned.

* In ''[[Anime/NeonGenesisEvangelion End of Evangelion]]'', [[spoiler:Unit-01, which harbors the soul of Yui Ikari, becomes fossilized as it drifts through space, and is said that it would go on to outlast the sun and the moon, an eternal testament to the existence of the human race.]]

* ''ComicBook/TheUltimates''
** The newly thawed out Captain America is despondent over how different things are. Technology has advanced massively, his high school friends, fiance and army buddies are in their 80s and modern morality is completely different than the 1940s. That is until Nick Fury points out the American flag over a cemetery and comments that one thing hasn't changed. (Well, except those two extra stars from 1959.)
** Tony Stark is getting rid of all his expensive souvenirs, and one of them is perfect for the newly reborn Captain America: the helmet he used during the war.

* ComicBook/VandalSavage acts as this sometimes for the DCU, since his complete unkillability allows him to survive pretty much any changes that would kill off everyone else.

* In the Franchise/MarvelUniverse, every reality has a version of [[PhysicalGod Owen Reece, the Molecule Man]]. [[spoiler:This is because [[EldritchAbomination the Beyonders]] deliberately created him as a constant as part of their deranged experiment to [[OmnicidalManiac destroy the multiverse]]. The death of a Molecule Man destroys the reality he's in, so they're planning to trigger the self destruct of ''every'' Molecule Man to cause a chain reaction that obliterates existence.]]
* ''ComicBook/BlackScience'' is about a group of dimensionauts who get sent on a journey across the multiverse. As they travel from reality to reality, patterns begin forming; Grant [=McKay=] always invents a device to travel through dimensions, the device is always sabotaged, [[spoiler:Kadir]] is always the saboteur, and, most worryingly, [[spoiler:the kids always seem to die.]]

* Bishop in ''ComicBook/AgeOfApocalypse''. When Legion accidentally killed Charles Xavier in the past, drastically altering the timeline where Apocalypse rose sooner than expected, took over America and reduced the [[CrapsackWorld world into a ruined husk]], Bishop was the only one to have retained his memories from the original timeline since he was a time traveler from a distant future and an chronal anomaly of his own right. He tries to SetRightWhatOnceWentWrong, even though this means the [=AoA=] timeline would cease to exist.

* The Christopher Reeve movie ''Film/SomewhereInTime'' features an elderly hotel employee who recognizes the hero from his childhood -- much to the hero's confusion, because from his perspective that event hasn't happened yet (he later goes back in time and meets a boy in the lobby who is clearly the same guy).
* In ''Film/{{Inception}}'', the folks who enter dreams carry a "totem", a small personal item that they alone know the exact size and weight of, to help them remember if they are in reality or dream state if need be. For instance, lead protagonist Dom carries a top that will spin endlessly in a dream, but topple in reality. Growers of EpilepticTrees may find some fertilizer in the observation that [[spoiler:the viewer does not see it topple before the movie cuts to credits]]. [[spoiler:Although WordOfGod states that eventually it does.]]
* The Statue of Liberty in the ''Film/PlanetOfTheApes1968'' movie that features so prominently in its famous EarthAllAlong ending.

* In the Creator/GeorgePal version of ''[[Film/TheTimeMachine1960 The Time Machine]]'', the protagonist finds a couple of constants during his early trips into the near future, including his friend Filby, and a shop near his laboratory that is featured in the time-travel montage whipping through a succession of window displays (later spoofed in the Literature/{{Discworld}} series, as described below). However, on his main excursion into the distant future he finds that everything has changed.
* In the Guy Pierce version of ''[[Film/TheTimeMachine2002 The Time Machine]]'', he meets an AI librarian from the New York Public Library who is still there in the overgrown, recognizable ruins of New York thousands of years later.

* Like ''Franchise/StarTrek'' below, ''Franchise/StarWars'' gives the audience a few constants when telling a story in a new time period: ''Film/ThePhantomMenace'' has no Rebellion and no Empire, with a strange Republic and Trade Federation in their places; but we know it's the same 'verse because we see Obi-Wan from the beginning, and Artoo, Threepio, Yoda, Tatooine (including Jabba the Hutt), [[StartOfDarkness Anakin]], and [[BigBad Palpatine]] later on.

* Inverted in the James Garner film, ''[[Film/ThirtySixHours1965 36 Hours]]''. The existence of something that should have vanished in a few days, [[spoiler: a paper cut]], is what convinces Maj. Pike, that he ''hasn't'' spent the last few years in a fugue state, as his German interrogators are trying to convince him he has in order to extract information from him.

* In ''Literature/TimeSpiral'', the type of time travel that Karn uses to go back in time to when he can seal the rift in Tolaria requires a solid link of related memories going back to when he needs to travel to. He uses his memories of his friendship with Jhoira.
* Marvin the Android serves as TheConstant in ''Literature/TheRestaurantAtTheEndOfTheUniverse'' (both the book and the place) over a few hundred million years. He's understandably bitter about it.
* In Susan Cooper's novel ''Literature/TheDarkIsRising'', the immortal Will Stanton meets the character Hawkin hundreds of years in the past. Hawkin undergoes a FaceHeelTurn and becomes the Walker, condemned to WalkTheEarth until it's time for him to fulfill his destiny in the present.
* In Creator/DianaWynneJones's ''Literature/TheHomewardBounders'', the Old Fort -- in particular, the statue on the grounds -- are the Constant. [[spoiler:So are the canal arches, and the sign identifying the former Churt House.]]
* Katharine Kerr's ''{{Literature/Deverry}}'' series:
** In ''Daggerspell'', a battle is fought among the ruins of a fortress at the edge of the grasslands. Several books later, we are shown in ''A Time of Exile'', in a story set a few hundred years prior, how the building of that fortress started a small war, and why it was abandoned. Brangwen's grave is another straight example.
** Averted when Nevyn, now a royal adviser, tries to find his old quarters in the royal brooch in Dun Deverry -- and cannot, because the complex has been repaired and expanded so many times over the centuries since he was condemned to WalkTheEarth.

* In Creator/UrsulaKLeGuin's short story "April in Paris", the protagonists occupy the same apartment in different centuries. Notre Dame is another Constant.
* In ''Literature/TheTimeTravelersWife'', Claire generally serves as Henry's Constant as he jumps around in time.
* In Creator/HBeamPiper's ''Lord Kalvan of Otherwhen'', the absence of an expected constant -- the stone quarries of an area of Pennsylvania that the protagonist knows quite well, and which could not have eroded while leaving the local geography intact -- tips him off to the fact that he has ''not'' [[TimeTravel travelled into the far future]] as he previously thought, but is in an AlternateUniverse.
* ''Literature/{{Discworld}}'':
** Lampshaded in ''Literature/WyrdSisters''. The biggest expense of TimeTravel is finding a fashion store that will remain open for 50 years in the exact same place, keeping the same mannequin in the display window.
** [[InvertedTrope Inverted]] in ''Literature/{{Night Watch|Discworld}}''. Sam Vimes ends up in the past after a magical accident, and has to keep things on-track while a criminal who went with him is messing everything up. Right when he's most despairing of ever getting back to where he belongs, [[spoiler: a History Monk brings him his silver cigar case, a gift from the wife he doesn't have yet and a reminder that his "future" is real and has already happened.]] On the other hand, many of the important cast members' past selves feature in the story: Fred Colon, M(r)s. Palm, Young Vimes, [[spoiler: Vetinari]]...
* A ''Franchise/StarWars'' novel has someone who was nearly killed at the end of the Clone Wars and put into stasis for at least half a century, awaking long after the ''original'' movies. With almost everyone he knew long dead and the galaxy having gone through several wars and governments, he decides to search for a specific Constant, the YT-1300 freighter he was flying on the mission where he nearly died - the ship that has since come to be known as the ''Millennium Falcon''.
* Creator/RobertRankin's Brentford series has Professor Slocombe, who is implied to have been Merlin and have worked with Sherlock Holmes. Also, the Flying Swan, which shows up on 15th century maps.
* In the Usborne Puzzle Adventure ''The Vanishing Village'', the protagonists must find help an 18th century village that's stuck in limbo. The only way they can get into the past is to bring something that originated in the village with them from the present day. It's a spoon, weirdly enough.
* In the ''Literature/{{Bolo}}'' story "The Night of the Trolls" by Creator/KeithLaumer, the protagonist comes out of a long stretch as a HumanPopsicle to find that society has collapsed. The first friendly person he meets in the new world is an old man who turns out to be his son, aged considerably in the 80 or so years since the protagonist's stasis began.
* The old Hermit in ''Literature/ACanticleForLeibowitz'', though his immortality is never explained in the book itself. However, most commentators agree that the final section of the book pretty much comes out and says that he's the [[FlyingDutchman Wandering Jew]].
* From ''Literature/InTheKeepOfTime'', Smailholm Tower. In an unusual variation, it is ''also'' the "time machine", as it were. The interesting implication of this is that the key can only take time travelers to a time period where the tower exists, not before its construction or after it collapses.

* OlderThanRadio: After sleeping for 20 years, RipVanWinkle is dismissed as just a loony old man until he is recognized by his daughter, now grown with a family of her own.
* In ''Literature/TheRedemptionOfAlthalus'', when the title character first goes to the House At the End of the World, he passes a particular dead tree, when he leaves the House, 2500 years later, the same dead tree is still there, The Goddess Dweia says the gods keep the tree around as a landmark.
* Used as a plot point in one ''Literature/{{Animorphs}}'' book, where the kids manage to use a vision of a BadFuture shown to them by the Ellimist to find out the location of the Yeerk Pool. In the vision (where they see what their city would look like in the aftermath of a full-scale Yeerk takeover) they notice that there's just one building in their city left standing, and they realize that the Yeerk Pool's exterior is the one building that the Yeerks wouldn't bomb if they ever launched a full-on attack.
* ''Franchise/TolkiensLegendarium'':
** Elrond Half-Elven serves as the Constant for the Númenoreans/Dúnedain: because his brother Elros was their first leader. No time travel is involved here. He just remembers literally all of them due to being immortal himself. He is a constant presence in their lives, most Princes of Númenor went to live with him for a time before assuming the throne.
** Galadriel serves as a Constant for the stories. She witnessed the events of the Quenta Silmarillion (Part III of ''Literature/TheSilmarillion''), and indeed this story ''seems'' to be her account of the events because we are privy to details of events that involve her or her siblings, but conversations between other characters often get glossed over (for example, everything said between Maedhros and Fingon is paraphrased except for Fingon's prayer to Manw&ediaresis;, but we get the full conversation between Thingol and Angrod even though the two events are theoretically of equal importance.) This would also explain why although the Battle at Alqualondë is described very matter-of-factly (as if by an eyewitness), Fingolfin's duel with Morgoth is described in a style resembling a legend with numbers that seem somewhat suspicious. Galadriel was present for the first battle, but did not witness the second one (and it specifically says the Eldar do not talk about it). She is then a minor character in both ''Literature/TheHobbit'' and ''Literature/TheLordofTheRings''.
** Círdan the Shipwright is one in-universe. He has been around in so long (since the elves first awakened at the place they were created, so for tens of thousands of years, making him the oldest known elf still there at the time of LOTR) that he is the only elf ever mentioned that has managed to ''grow an actual long grey beard.'' And he (or one of his two ports) is at the very least mentioned in almost every major work to do with Middle-earth.
* In ''Literature/ThreeDaysToNever'', the Constant is an integral part of time travel: the method to travel to a particular point in time requires an object that was present there and underwent a significant change at the target moment.
* In Brian Aldiss's ''Hothouse,'' the world is utterly bizarre and unrecognizable to the novel's audience. But at the end of one chapter, the characters see a structure that means nothing to them, but the modern reader can recognize as--not a specific landmark, but an ancient castle, or the ruin of one.
* Creator/StephenBaxter's ''Manifold'' series:
** Reid Malenfant himself is a constant throughout the 'series', each of which takes place in a universe with different starting conditions. He is the main character in ''Literature/ManifoldSpace'' and ''Literature/ManifoldTime'', and a primary character in ''Literature/ManifoldOrigin''. Always a mustered out NASA astronaut, his history diverges heavily in every book, but his drive for humanity's future and his confused love for his estranged wife remains a constant theme.
** In ''Literature/ManifoldSpace', Reid Malenfant and Madeleine Meacher becomes increasingly isolated from mankind as they are thrown system to system at the speed of light. Every time they return to Sol, [[FishOutOfTemporalWater mankind has changed]] and not necessarily for the better. However, every time they return they cross paths with Nemoto, a manipulative, paranoid, and [[TheAgeless seemingly ageless]] Japanese astronomer who works behind the scenes to protect mankind from her 'alien threat'.

* In ''Literature/TimeAndAgain,'' the hero ''must'' use a Constant to travel through time: His departure and arrival must be in the same structure. At one point, on the run from police, he ducks into the Statue of Liberty's disembodied hand (This was in 1880, and the statue hadn't been erected yet, but the hand holding the torch was on display in Madison Square Park in Manhattan for several years during this time.) and uses it to travel to the completed statue in the present.

* Hoid in ''Literature/TheCosmere''. On every world and in every era, he appears in some way. His role varies wildly from story to story -- HeroOfAnotherStory, AllPowerfulBystander, TheTrickster, GreaterScopeParagon, [[GreaterScopeVillain Greater-Scope]] ''[[GreaterScopeVillain Villain]]'' -- but he’s always involved somehow. This actually [[NotHisSled made it rather shocking]] when there was a story (''Literature/ShadowsForSilenceInTheForestsOfHell'') where he ''doesn’t'' appear, or even get mentioned.

* ''Series/BabylonFive'' has an Interplanetary Constant rather than a Temporal Constant. According to G'Kar every known planet has a food that's identical to Earth's Swedish Meatballs.
* ''Series/TheOuterLimits1995'':
** In "[[Recap/TheOuterLimits1995S2E21VanishingAct Vanishing Act]]", Trevor [=McPhee=] travels forward in time to 1960, 1970, 1980 and 1990. He meets his wife Theresa, who eventually divorces him due to his unavoidable absences, in every time period. Trevor also meets Theresa's new husband Ray Carter in 1960, 1970 and 1980. As Ray died in 1988, he only sees a video recording of him in 1990. Trevor's son Mark, who was conceived during his brief sojourn in 1960, is present from 1970 onwards.
** In "[[Recap/TheOuterLimits1995S5E12Tribunal Tribunal]]", Leon Zgierski and Karl Rademacher are present as young men in Auschwitz in 1944 and as elderly men in UsefulNotes/{{Philadelphia}} in 1999.
** In "[[Recap/TheOuterLimits1995S7E15TimeToTime Time to Time]]", Angie Palmer is present in UC Berkeley in both 1969 and 1989.
* The GrandFinale of ''Series/KamenRiderZiO'' reveals that every world has at least one Kamen Rider to represent it. Without one, the world would be lead to ruin. [[spoiler:Even as the BigBad who's destroying worlds to save his learns of this, he decides to keep destroying worlds anyway.]]

* The ruined tower in Sheratan in ''VideoGame/BatenKaitos Origins'' serves as a constant for Sagi, who can eventually use it to travel back and forth in time [[spoiler:due to housing a spirit who was alive back then]].
* Happens several times to the immortal Kaim, in ''VideoGame/LostOdyssey''. A couple of incidents in the 'Dreams of a Thousand Years' section involve him meeting someone as a child, then crossing their paths again, 60, 70 or 80 years later, where they're old and dying, and he's still as young as ever. In the main game story, he also meets a wise old king - whom, as it turns out, he first met when he was a brash young prince, and taught a few things about combat, survival, and life in general.
* In ''VideoGame/DayOfTheTentacle'', the same house exists for over 400 years, from the days of the FoundingFathers to the future where the tentacles have taken over the world, although it's much more metallic in the future. Also, many objects in the house can be found in more than one time period. This is often used by the main characters to affect one or more future time periods. For example, since only inanimate objects can be passed through the [[OurTimeMachinesAreDifferent Chron-O-John]], the only way to send a hamster to Laverne in the future is to put it in the [[HumanPopsicle freezer]], which is still around 200 years from now. Apparently, no one has bothered to look inside in all this time. The time machine is still in the basement in the future (though it's broken and useless), and the laundry room doesn't change in the slightest - the coin-operated dryer Bernard sets running in the present is still going two hundred years later (he fed it a ''lot'' of change).

* Across both wildly divergent timelines in the ''VideoGame/CommandAndConquer'' series, ''[[VideoGame/CommandAndConquerTiberium Tiberium]]'' and ''[[VideoGame/CommandAndConquerRedAlert Red Alert]]'', there is a corporation called Futuretech. This was introduced in the last respective entries of the series. In the ''first'' respective entries the constant was Kane (at the time the plan was for ''Red Alert'' to be a prequel to ''Tiberian Dawn'', though that got lost when ''Red Alert 2'' was made).
* In the ''VideoGame/BioShock'' series, [[spoiler: there is always a man, a lighthouse, and a city, no matter what universe.]]

* Dracula's castle in ''Franchise/{{Castlevania}}'' games is [[{{Bizarrchitecture}} an ever-changing structure]] ("[[ChaosArchitecture a creature of chaos]]" as ''[[VideoGame/CastlevaniaSymphonyOfTheNight Symphony of the Night]]'' puts it), but the corridor in its entrance stays the same. Also, the approach to Dracula's throne room generally includes a long staircase going upward from right to left. Sometimes other parts of the castle will remain the same between specific incarnations. For example, the clock tower in both ''[[VideoGame/CastlevaniaRondoOfBlood Rondo of Blood]]'' and ''Symphony of the Night'' are very similar in layout.
* Promotional material for ''VideoGame/FiveNightsAtFreddys3'' implies Freddy Fazbear intends to become this trope. [[spoiler:"I am still here."]]
* In ''VideoGame/Fallout4'', the Protagonist is Cryogenically frozen, their spouse killed, and their son kidnapped. Their robotic butler, Codsworth, exists as a constant between the pre-war and post-war times. The Vault-Tec Salesman who sold you your place in the Vault can also be found and recruited, however he has undergone 'Ghoulification' due to the radiation damage.

* ''Webcomic/{{Narbonic}}'' has one where Dave has to find a Constant, so he can get returned to the present. [[spoiler: Getting slapped/punched by a girl works!]]

* Jones (aka Wandering Eye) is a constant in ''Webcomic/GunnerkriggCourt''. In the flashbacks where the parents of the main protagonists are shown in their school days, Jones is there, appearing exactly as she does in the present. This (along with the inhuman speed and strength Jones had already demonstrated) led to fan speculation that Jones was a particularly humanoid robot, which author Tom Siddell shot down in comments without revealing any more than that. [[spoiler: When Antimony finally gets the story out of her, it turns out that Jones has been around literally since the Earth was formed. Even she doesn't know what she really is.]]

* ''WesternAnimation/LoveDeathAndRobots''. The episode "Sonnie's Edge" takes place in a vandalised and derelict St Paul's Cathedral, now repurposed as a fight ring for remotely-controlled bioengineered beasts, in the midst of a [[NeonCity neon-lit future London]].
* Similar to ''Avatar'' but across a much longer time period, there is an episode of ''WesternAnimation/SamuraiJack'' where Jack visits a temple he had been to in the past. Not only do the martial artist students practice the same traditions, but there is even a monk there, thousands and thousands of years old, that Jack met when he was there.
** And when Jack finally finds his homeland.

* Demona and Macbeth in ''WesternAnimation/{{Gargoyles}}'' had a spell laid on them around 1025 AD which has rendered them immortal.
* In ''WesternAnimation/TheFairlyOddParents'', when Timmy changed the past and ended up living in a terrible foreign country called Ustinkistan (inside hasn't been invented, the nights last 11 months, during which werewolves are on the prowl, and the last boat to ever leave the country sailed fifty years ago), Timmy was forced to use a turnip time machine to go back in time and change the past back. After using the machine, Timmy noticed that everything was still the same, leading him to believe that the time machine didn't work. Wanda then tells him it did and he was now fifty years in the past. As she noted "Not much changes here in Ustinkistan".

* ''Franchise/{{Nasuverse}}'': The series actually [[JustifiedTrope justifies]] this with the Quantum Time-Lock system put in place by [[DeusEstMachina The World]]. . As a limited amount of "water" exists to sustain so many worlds without the universe effectively overloading on the sheer weight of possibilities, Quantum Time-Locks happen every once a hundred years or so to ensure that Constants exist present in all other timelines (e.g. Camelot falling). [[CuttingOffTheBranches Any other timelines that have anything different happen are purged altogether in a process known as 'pruning']]. However, while there exists several Quantum Time-Locks across human history, the ''median'' of which these Time-Locks happen can be extraordinarily variant to a variety of possibilities; it's just that the Quantum Time-Locks are a means of ensuring the most prosperous timelines for humanity survive, and any that have grown past the point of being able to be changed are as a result pruned.

* ''Franchise/{{Nasuverse}}'': The series actually [[JustifiedTrope justifies]] this with the Quantum Time-Lock system put in place by The World. As a limited amount of "water" exists to sustain so many worlds without the universe effectively overloading on the sheer weight of possibilities, Quantum Time-Locks happen every once a hundred years or so to ensure that Constants exist present in all other timelines (e.g. Camelot falling). [[CuttingOffTheBranches Any other timelines that have anything different happen are purged altogether in a process known as 'pruning']]. However, while there exists several Quantum Time-Locks across human history, the ''median'' of which these Time-Locks happen can be extraordinarily variant to a variety of possibilities; it's just that the Quantum Time-Locks are a means of ensuring the most prosperous timelines for humanity survive, and any that have grown past the point of being able to be changed are as a result pruned.

* Creator/JRRTolkien's Literature/MiddleEarth:

** The Clock Tower is a major example of this trope, as it appears under construction [[Film/BackToTheFuturePartIII in 1885]], working just fine [[Film/BackToTheFuture in 1955]], broken and run-down [[Film/BackToTheFuture in 1985]], transformed into a casino-hotel in the [[Film/BackToTheFuturePartII alternate 1985]], and as a piece of high-tech modern art [[Film/BackToTheFuturePartII in 2015]].
** Doc Brown serves as one in the [[Film/BackToTheFuture first film]], as well, more so than Marty's parents or Biff, as he is aware that Marty has been time-travelling.

* ''{{Cheers}}'' has an entirely mundane example in the form of resident barfly Norm Peterson. He's been coming to the titular bar for so long there are at least two separate occasions where a person who hasn't been there in years or even decades comes back and instantly recognizes him. Another time, he claims he used to work out at a gym that was next door to Cheers none of the others remember, and says it was torn down to build a bookstore, then a bakery, then a bank...

* There are several in ''{{Series/Dark}}'', thanks to taking place entirely in the same town, but the most frequently-recurring is the Winden Cave entrance, which appears in every single time period from the 1800s all the way to the far apocalyptic future where it’s the only landmark left among an endless desert.

* The Clock Tower in ''Franchise/BackToTheFuture'' in a major example of this trope, as it appears under construction [[Film/BackToTheFuturePartIII in 1885]], working just fine [[Film/BackToTheFuture in 1955]], broken and run-down [[Film/BackToTheFuture in 1985]], transformed into a casino-hotel in the [[Film/BackToTheFuturePartII alternate 1985]], and as a piece of high-tech modern art [[Film/BackToTheFuturePartII in 2015]].

** In ''Literature/TheSilverChair'' the heroes are directed by Aslan to go to the Ruined City of the Giants and look for [[PlotCoupon a sign]] that would tell them where to go. Not seeing anything, they are trapped in a snowstorm and forced to hide in a series of trenches. They [[ThatsNoMoon realize their mistake later]] when [[TheRuinsICaused returning to the site]], they see the trenches were actually letters on a giant inscription:
--> '''Though under earth and throneless now I be, Yet, while I lived, all earth was under me.'''
** The city was gradually reduced to ruins, until all that was left was the inscription. Finally all that remained of the inscription was the final two words: "UNDER ME."
*** The long version is according to the antagonist, who is clearly trying to distract the heroes from their quest. The literal meaning is clear: Look under the inscription.
** And in ''Literature/PrinceCaspian'', the Pevensies return to Narnia and Susan finds one of their old chess pieces, and they realize that they're in the ruins of Cair Paravel.

* The old Hermit in ''Literature/ACanticleForLeibowitz'', though his immortality is never explained.
** Most commentators agree that the final section of the book pretty much comes out and says that he's the [[FlyingDutchman Wandering Jew]].

* Across both wildly divergent timelines in the ''VideoGame/CommandAndConquer'' series, ''[[VideoGame/CommandAndConquerTiberium Tiberium]]'' and ''[[VideoGame/CommandAndConquerRedAlert Red Alert]]'', there is a corporation called Futuretech.
** This was introduced in the last respective entries of the series. In the ''first'' respective entries the constant was Kane (at the time the plan was for ''Red Alert'' to be a prequel to ''Tiberian Dawn'', though that got lost when ''Red Alert 2'' was made).

* Dracula's castle in ''Franchise/{{Castlevania}}'' games is [[{{Bizarrchitecture}} an ever-changing structure]] ("[[ChaosArchitecture a creature of chaos]]" as ''[[VideoGame/CastlevaniaSymphonyOfTheNight Symphony of the Night]]'' puts it), but the corridor in its entrance stays the same. Also, the approach to Dracula's throne room generally includes a long staircase going upward from right to left.
** Sometimes other parts of the castle will remain the same between specific incarnations. For example, the clock tower in both ''[[VideoGame/CastlevaniaRondoOfBlood Rondo of Blood]]'' and ''Symphony of the Night'' are very similar in layout.

** Doc Brown serves as one in the [[Film/BackToTheFuture first film]], as well, moreso than Marty's parents or Biff, as he is aware that Marty has been time-travelling.

** And in ''Literature/PrinceCaspian'', the Pevensies return to Narnia and Susan finds one of their old chess pieces, and they realize that they're in the ruins of Caer Paravel.

** White London is slowly being drained of its magic and its life energy [[spoiler: due to it's proximity to Black London]]. The White dimension is currently undergoing a bloody, neverending civil war, with the leader (or leaders) of White London changing every few years. People there are willing to do ''anything'' to get a bit of magic power.

** Nelson the Bartender from ''Series/{{Life On Mars|2006}}'' also appears at the end of ''Series/AshesToAshes2008'' becuase [[spoiler: he is a holy power and is accepting Alex, Shaz, Chris and Ray into heaven.]]

** There is also the Watchtower which, in a subtle ChekhovsGun, has [[ColonyDrop survived reentry]] to crashland in the jungle.

** In "[[Recap/DoctorWhoS31E13TheBigBang The Big Bang]]", [[spoiler: events are put into place that makes Amy Pond the constant for the entire universe.]]

* ''WesternAnimation/{{Futurama}}'' has several Constants: the subterranean ruins of New York, the pizzeria where Fry used to work, the various [[PeopleJars heads of celebrities preserved in jars]], and so on. The biggest one is probably [[spoiler:Nibbler, who was responsible for Fry being frozen a thousand years earlier]]. And Fry's dog...who we'll skip over before we start to [[TearJerker tear up]].

* The Sacred Tree in ''Manga/InuYasha''. In the past, it's where Kagome meets the titular Inuyasha; hundreds of years in the future, it's still tended by her grandfather, even though a modern city has grown up around it. The nearby Bone-Eater's Well also exists in both times and acts as a PortalToThePast while it's at it.

* The TropeNamer is the ''Series/{{Lost}}'' episode "[[Recap/LostS04E05TheConstant The Constant]]", in which Desmond is undergoing rapid MentalTimeTravel between two times in his life and must find a Constant in the two times in order to avoid insanity and death. It's [[spoiler:his girlfriend Penelope]]. In the same episode, Daniel Faraday discovers a note in his journal saying that if the same thing ever happens to him, he will use [[spoiler:Desmond]] as his Constant.
* Although there's no TimeTravel involved, [=McCoy=] appears in "Encounter at Farpoint", the first episode of ''Series/StarTrekTheNextGeneration'', as a reminder that the two series take place in [[TheVerse the same universe]] but different times.
** The same idea occurs with all the other series of ''Franchise/StarTrek'' as well, with a character from a preceding series showing up in the first episode of the new series (Picard in ''[[Series/StarTrekDeepSpaceNine Deep Space Nine]]'', Quark in ''[[Series/StarTrekVoyager Voyager]]'', Spock (and a reference to an Admiral Archer) in [[Film/StarTrek2009 the 2009 reboot]]. ''[[Series/StarTrekEnterprise Enterprise]]'', due to taking place earliest in the continuity, used Zefram Cochrane from ''Film/StarTrekFirstContact''.
** In the two-part ''[[Series/StarTrekTheNextGeneration Next Generation]]'' episode "Time's Arrow", the long-lived Guinan is the link between times (along with Data's severed head).
** The ''Next Generation'' two-parter "Unification", created for an anniversary and featuring Spock, who is used to link the past and the present. Spock (specifically, Leonard Nimoy as Spock) is arguably this for the franchise as a whole, since he also appears in the 2009 reboot movie, where he actually serves to make it clear that the reboot is taking place in a ''different'' timeline, which is nevertheless at least related to the TOS one.
** The Guardian of Forever in the original series episode "The City on the Edge of Forever" claims to be this for almost all sentient history. "Since before your sun burned hot in space, I have awaited a question."

** In "Vanishing Act", Trevor [=McPhee=] travels forward in time to 1960, 1970, 1980 and 1990. He meets his wife Theresa, who eventually divorces him due to his unavoidable absences, in every time period. Trevor also meets Theresa's new husband Ray Carter in 1960, 1970 and 1980. As Ray died in 1988, he only sees a video recording of him in 1990. Trevor's son Mark, who was conceived during his brief sojourn in 1960, is present from 1970 onwards.
** In "Tribunal", Leon Zgierski and Karl Rademacher are present as young men in Auschwitz in 1944 and as elderly men in UsefulNotes/{{Philadelphia}} in 1999.
** In "Time to Time", Angie Palmer is present in UC Berkeley in both 1969 and 1989.

* Promotional material for ''Videogame/FiveNightsAtFreddys3'' implies Freddy Fazbear intends to become this trope. [[spoiler:"I am still here."]]
* In ''VideoGame/{{Fallout 4}}'' the Protagonist is Cryogenically frozen, their spouse killed, and their son kidnapped. Their robotic butler, Codsworth, exists as a constant between the pre-war and post-war times. The Vault-Tec Salesman who sold you your place in the Vault can also be found and recruited, however he has undergone 'Ghoulification' due to the radiation damage.

[[folder:Web Comics]]

** Galadriel serves as a Constant for the stories. She witnessed the events of the Quenta Silmarillion (Part III of ''Literature/TheSilmarillion''), and indeed this story ''seems'' to be her account of the events because we are privy to details of events that involve her or her siblings, but conversations between other characters often get glossed over (for example, everything said between Maedhros and Fingon is paraphrased except for Fingon's prayer to Manw&ediaresis;, but we get the full conversation between Thingol and Angrod even though the two events are theoretically of equal importance.) This would also explain why although the Battle at Alqualond&ediaresis; is described very matter-of-factly (as if by an eyewitness), Fingolfin's duel with Morgoth is described in a style resembling a legend with numbers that seem somewhat suspicious. Galadriel was present for the first battle, but did not witness the second one (and it specifically says the Eldar do not talk about it). She is then a minor character in both ''Literature/TheHobbit'' and ''Literature/TheLordofTheRings''.

* There are several in ''Series/Dark'', thanks to taking place entirely in the same town, but the most frequently-recurring is the Winden Cave entrance, which appears in every single time period from the 1800s all the way to the far apocalyptic future where it’s the only landmark left among an endless desert.

If the time traveled was too short, there may be so many Constants that it's unremarkable. For example, it's not uncommon for the entire cast from the past to switch to FutureBadass versions of themselves in the future. On the other hand, there is no minimum time difference -- a city may be reduced to an unrecognizable place overnight by a terrible weapon, except for The Constant--a famous statue or historic building--proving it was there. Or as Music/{{Nena}} would say, "If I could find a souvenir / Just to prove the world was here."

If the time traveled was too short, there may be so many Constants that it's unremarkable. For example, it's not uncommon for the entire cast from the past to switch to FutureBadass versions of themselves in the future. On the other hand, there is no minimum time difference -- a city may be reduced to an unrecognizable place overnight by a terrible weapon, except for The Constant--a famous statue or building--proving it was there. Or as Music/{{Nena}} would say, "If I could find a souvenir / Just to prove the world was here."

If the time traveled was too short, there may be so many Constants that it's unremarkable. For example, it's not uncommon for the entire cast from the past to switch to FutureBadass versions of themselves in the future. On the other hand, there is no minimum time difference -- a city may be reduced to an unrecognizable place overnight by a terrible weapon, except for The Constant proving it was there. Or as Music/{{Nena}} would say, "If I could find a souvenir / Just to prove the world was here."

If the time traveled is very long, the Constant will typically be a structure or an immortal rather than an ordinary person. If it is a person, it's usually the IdenticalGrandson or a variation thereof (such as MyGrandsonMyself).

* ''Series/BabylonFive'' has a Planetary Constant rather than a Temporal Constant. According to G'Kar every known planet has a food that's identical to Earth's Swedish Meatballs.

Not related to a high-ranking member of Providence from the ''VideoGame/{{Hitman}}'' series.

* ''WesternAnimation/LoveDeathAndRobots''. In "Sonnie's Edge" takes place in a vandalised St Paul's Cathedral--now repurposed as a fight ring for remotely-controlled bioengineered beasts--in the midst of a [[NeonCity neon-lit future London]].

** Averted when Nevyn, now a royal adviser, tries to find his old quarters in the royal broch in Dun Deverry -- and cannot, because the complex has been repaired and expanded so many times over the centuries since he was condemned to WalkTheEarth.

* The GrandFinale of Series/KamenRiderZiO reveals that every world has at least one Kamen Rider to represent it. Without one, the world would be lead to ruin. [[spoiler:Even as the BigBad who's destroying worlds to save his learns of this, he decides to keep destroying worlds anyway.]]