Horse

Horses are creatures mentioned before and after the Great War.

Background
References to the creatures can be found in dialogue, within terminals, and on world objects.

Fallout

 * Dane, one of the Children of the Cathedral, will mention horses in his ramblings.

Fallout 2

 * When talking to Ethyl Wright, the Chosen One may mention enjoying fermented milk from a mare, or female horse.
 * Lenny may exclaim, "I've got to talk to a man about a horse" before running away from combat.

Fallout 3

 * A horse toy called the Giddyup Buttercup was popular before the war. Advertisements describe the toy as being, "programmed to perfectly emulate the behavior of an actual horse."
 * A story titled the Guardians of Gillyfrond mentions a toy variant of the creature, stating "there then rose a rustle and rumble from all corners of the room, as rocking horse and railway car, bookend and baby doll, toy and game alike all blossomed into impossible life."

Fallout: New Vegas

 * Swank refers to New Vegas as a "wild horse" when the Courier asks for his thoughts on Robert House.
 * A book entitled Pretty Pretty Horsies: A History of the Mongol Empire is a quest item used to convince the Great Khans to break their alliance with Caesar's Legion, by revealing the past of their historical inspiration.
 * There is a horse toy shown on the Big Ranch Nevada State Lotto billboard in the Mojave Wasteland.
 * Arcade Gannon refers to those preparing for the Second Battle of Hoover Dam as "warhorses."
 * Festus offers the Courier an opportunity to play a game called Lucky Horseshoes.
 * On the cover of Tæles of Chivalrie, a knight can be seen riding a horse while fighting a dragon.
 * The former inhabitants of Vault 19 found "enough sedatives to kill a horse" in the vault clinic.
 * Some Great Khan graffiti depicts a rider on the horse.
 * The Dead Horses tribe and their locations at Dead Horse Point and Dead Horses camp are mentioned.
 * The war clubs used by the Dead Horses are the shape of a horse head.

Fallout 4

 * There is a drawing of a horse, chicken and cow used in a framed picture near Bunker Hill. The same drawing appears at an unmarked trapper outpost northwest of the MS Azalea, in the add-on Far Harbor.
 * A horse is part of the Paul Revere Monument in Boston.
 * Nick Valentine uses the phrase "hold your horses" several times.
 * Cait mentions that she is not one to "look a gift horse in the mouth."
 * Supervisor Greene uses the phrase "just hold your horses, little lady" when addressing Supervisor White at Graygarden.
 * Robert MacCready references the Ancient Greek's Trojan horse.
 * The Easy City Downs‎‎ Racetrack and Clubhouse featured horse races before the war, and horses are depicted on its signage.
 * Deacon tells the Sole Survivor to put their money on the pony Black Velvet as they approach the racetrack, and Curie asks, "Is this... horse racing?"
 * Codsworth comments on the racetrack and robots reprogrammed as race horses.
 * Codsworth also uses the exclamation "horsefeathers" and recites a nursery rhyme mentioning the creatures.
 * Arlen Glass' terminal mentions variation ideas for the Giddyup Buttercup, including pink paint, a Hubris Comics Mechanist's robot horse, and Nuka-Cola limited-edition red horse.
 * If the Sole Survivor helps Far Harbor's Cassie Dalton avenge her family, she will comment about a horse and riding off into the sunset.
 * Napoleon's ceremonial parades on horseback throughout Europe are mentioned on a plaque in the Wixon's Shovel Museum.
 * Members of the Pack ask one another what a horse was, and if it was similar to a large dog that one could ride.
 * Porter Gage mentions horses twice, once in a reference to betting and once telling the Sole Survivor to "have fun getting shot from off the top of your high horse."
 * The Giddyup Kid asks for help corralling horses. If dressed as the Silver Shroud, the Sole Survivor can agree to help, stating, "Horses gone missing? The Silver Shroud shall ensure this is not part of some more diabolical plot." If successful, Giddyup Kid, Sheriff Hawk, and Sheriff Eagle will express their gratitude.
 * In the Braxton visit holotape, the general uses the phrase, "you and I both know that's a load of horse shit" when speaking with John-Caleb Bradberton.

Fallout 76

 * There is a horse on the sign for the Flatwoods Tavern.
 * Story Time Miss Nanny mentions horses during the story "Cinderella" that she will tell to the Vault Dweller as part of a random encounter.
 * Horse trailers are found on roadways and in barns around Appalachia.
 * Thurston Wellingham mentions a fully-staffed horse riding stable available to children at Bolton Greens.
 * Several different varieties of horses serve as part of the carousel ride at Camden Park.
 * The Natural Resistance perk card description reads, "You're healthy as a horse! Or deathclaw."
 * An Appalachian audio tour station at Uncanny Caverns mentions Poseidon, the ancient Greek god of the sea, earthquakes, storms, and horses.
 * Horseshoes are mentioned in the Prickett's Fort audio tour.
 * In Berkeley Springs Station, the wallpaper is patterned with pictures of horses.
 * Miranda Vox wrote that Raleigh Clay had been spotted outside of his bunker appearing, "healthy as a horse."
 * Horses are mentioned in the note PIONEERBOOK: Foreward.
 * A location in Appalachia is named Horse Creek Petroglyphs.
 * Horses are mentioned in the Pioneer Scout camp exams, including references to the "Trojan Horse," the word "horseplay," and "horse slicer."
 * Scout Leader Jaggy laments about missing the sight of horses in Appalachia.
 * Vault 51 personnel Brianna Ware was a former horse trainer.
 * Johnny Weston uses the phrase, "you just keep beating that dead horse, don't you?"
 * Molly uses the phrase "cool your horses" during the quest From Russia With Lev.
 * The settler wanderer uses a metaphor of "getting on a white horse" for rescuing a settler.
 * Maggie Stern brags that she could take on the Vault Dweller with one hand while brushing her toy pony with the other.
 * Rose derisively refers to Meg Groberg as being on "her high horse" during Strange Bedfellows.
 * Vinny Costa uses the phrase, "slow your horses."

Other

 * In the promotional graphic novel All Roads, an NCR soldier seen in Chance's flashback of the Bitter Springs Massacre is riding a horse.
 * Komodo Man uses the phrase, "Hold your bloody horses, mate."
 * Horses are referenced in the description of the Ol' Painless weapon in Fallout Shelter.
 * The note "Missing person: Greg Roethe," cut from Fallout 76, mentions that Greg has been missing since leaving on vacation to ride horses in Kentucky.

Behind the scenes
Joshua Sawyer stated during an October 2020 livestream that horses were never considered for implementation in Fallout: New Vegas, as they did not seem appropriate. He commented that he was not immediately familiar with the horses appearing as an error in All Roads, the concept of horses being completely extinct in Fallout, or Chris Avellone expressing it. He had "no idea" about this information, and that if he ever knew, it was "lost like dust in the wind."