There used to be a very vocal faction at the IMDb forums which reckoned that "all of DreamWorks' ideas were stolen from Pixar" (yes, all of them). At least two of their favorite examples were shown to be nonsense, as they were in production years before and only bore a superficial resemblance, and in any case one of them (Flushed Away) was actually an Aardman Animations movie — the DreamWorks involvement was minimal.
Everybody knows Aladdin was the first ever cartoon to have a Celebrity Voice Actor. Except Disney has been using celebrities in their films as far back as Pinocchio, which had Cliff Edwards as Jiminy Cricket; he would reappear shortly after it in Dumbo as Jim Crow. The Jungle Book is another pre-Aladdin example, having a nearly All-Star Cast thanks to Phil Harris (Baloo), Sebastian Cabot (Bagheera), George Sanders (Shere Khan), and Louis Prima (King Louie).
Even earlier was Rankin/Bass's The Last Unicorn, featuring Alan Arkin, Jeff Bridges, Mia Farrow, Angela Lansbury, and Christopher Lee.
It would be much quicker to list the Disney movies that are not based on an earlier fairy tale, book or legend. That will not stop some viewers from thinking Disney thought of them first, especially if it was not based on a fairy tale.
Disney's animated take on "Beauty and the Beast" isn't the first adaptation of the work to feature Animate Inanimate Objects — they can be seen in Jean Cocteau's legendary live-action film from 1946 and a Russian animated featurette from the same decade, both of which were adapting the detail in the source fairy tale that the castle seems to have no residents aside from the Beast, yet it's always meticulously maintained, food is plentiful, etc. The main difference, and it is significant, is that Disney's Enchanted Objects are fully-developed characters. The 1946 film is also the first adaptation to have a character who is a romantic rival for the heroine, and who tries to loot the castle and destroy the Beast in the climax, although Gaston is a much more developed and diabolical character than Avenant. Disney doesn't make a big point of acknowledging this film's influence on their version, but they occasionally do; they once considered doing a Direct-to-Video sequel to their version that would have had Gaston's brother, who would have been named Avenant as a direct reference, as the villain.
Walt Disney choosing the fairy tale as the basis for his first feature-length production goes back to his being impressed by a 1916 silent film version that adapted a 1912 Broadway play based on the story collected by the Brothers Grimm. The play and silent film share several details with the later Disney version:
Snow White is forced to work by her stepmother as a maid, in hopes of playing down the girl's beauty.
The prince and Snow White meet and fall in love before the Queen sends her away to be killed by the Huntsman, unlike in the original tale where he only appears at the end.
Snow White is led by a bird to the dwarfs' cottage, just like Disney's Snow White is led there by her animal friends.
The play is probably the first adaptation of the story in which the Queen's disguise as a peddler woman is the result of a magical transformation rather than Wig, Dress, Accent.
In the play, the youngest dwarf is a mostly silent character, though unlike Dopey he does have two lines. This particular dwarf never washes either, so when they realize there's a girl in their house, the others forcibly give him a bath just like Disney's dwarfs do to Grumpy.
The Disney version also seems to borrow a few details from Alexander Pushkin's 1833 poem ''The Tale of the Dead Princess and the Seven Knights," a Russian version of the tale retold in verse. Pushkin's poem also introduces the prince early on, has the princess clean the seven knights' house instead of eating their food the way the Grimms' Snow White does, and omits the queen's first two murder attempts, leaving only the poisoned apple.
Snow White and the Seven Dwarves is not actually the first full-length animated film. It is only the first color one. The first was the Argentinan political satire El Apóstol ("The Apostle") from 1917. It and its sequel Sin Dejar Rastro are lost films due to the only copies being destroyed in a fire. Of films that are known to still exist, 1926's The Adventures of Prince Achmed predates Snow White by eleven years. It's a silent feature that uses cut-out silhouettes against painted, colored backdrops. Disney's film is the first full-color and cel-animated feature, with a full music-and-dialogue soundtrack.
Jiminy Cricket is the sidekick in Disney's animated feature, Pinocchio, but his name isn't original — it's a pun playing off of a then-common expression that turns up in this one. When they first realize a stranger is in their cottage, the dwarfs whisper "Jiminy crickets!" in unison.
The Incredibles has a multiple dose of Older Than They Think on this very wiki; on the Headscratchers page, one troper claimed that Pixar got the idea of zero-point energy from Half-Life 2. Another then pointed out that The Incredibles came out first (albeit by only a few days), a third claimed that he had first come across the idea in a story in 1980, and a fourth pointed out that the idea was far older even than the latter story, having been devised by Albert Einstein and Otto Stern.
Toy Story has a cute and creative idea, the thought that toys actually come alive while their master is away. What many people don't know however is that the idea first appeared in several earlier children's classics:
Raggedy Ann premiered as a doll in 1915 and in storybooks in 1918. On a related note: Buzz Lightyear not realizing he's a toy? They already did that gimmick with Babette the French Doll in Raggedy Ann & Andy: A Musical Adventure - made in 1976 and released in 1977.
The Velveteen Rabbit, published in 1922. The book's climax shows its age, as it revolves around the rabbit's little boy owner contracting scarlet fever.
Jim Henson's 1986 The Christmas Toy not only uses the same basic "toys coming to life" scenario, but also revolves around a child's favorite toy worried about being replaced, and his new competitor is a space-themed action figure who doesn't realize she's a toy!
For more info on this trope, read When Toys Come Alive by Lois Rostow Kuznets. She has the whole history.
Spider-Man: Into the Spider-Verse has many things that fly over the heads of casual audiences that were actually in the comics, but the most notable is the idea of an adult Peter Parker given how every project before hand portrayed him as a high school or college student. Peter was actually a teenager for about two years in the comics, while most modern day adaptations simply focus more on him when he's younger.
A fair amount of first-time watchers have gone into Uglydolls thinking it's an entirely new franchise made to sell toys, or simply a cute rip-off of the Fugglers toyline. The movie itself is based on a 2001 toyline that was fairly popular in its heyday, only reviving in full for the movie.