According to Roger Ebert, An American Tail is one of the most depressing children's movies of all time—but try telling that to the millions of kids who adored Fievel Mousekewitz, his emigrating family, and the diverse cast of characters who (spoiler alert) helped reunite them. If you were one of them, read on for 12 not-so-depressing facts about the animated hit.

1. IT WAS DON BLUTH'S SECOND POST-DISNEY MOVIE.

Before striking out on his own, Don Bluth was an animator at Disney, working on Sleeping Beauty, Robin Hood, The Rescuers, and Pete's Dragon, among others. On September 13, 1979—his 42nd birthday—Bluth and fellow Disney animator Gary Goldman resigned from Disney in order to work on their own projects. They devastated the studio by taking 16 animators with them, resulting in an 18-month delay on The Fox and the Hound. Their first release, The Secret of NIMH, was a critical success, if not a commercial one—and it gained Bluth a very important fan: Steven Spielberg, who soon approached him about making An American Tail.

2. FIEVEL WAS NAMED AFTER STEVEN SPIELBERG'S GRANDFATHER.

Though Don Bluth originally thought the foreign name would be difficult for children to remember, the name "Fievel" was extremely personal to Steven Spielberg, so it stayed—Fievel was the Yiddish name of his grandfather, Philip Posner.

Spielberg's grandfather used to tell him stories about growing up in Russia, including one about how Jewish children were banned from attending secondary school. But they were allowed to sit outside and listen through open windows, which they did, even during snow and other inclement weather. A scene in the movie pays homage to the real Fievel's struggle for education when Fievel the mouse sadly watches American mice going to school.

3. FIEVEL'S AMERICAN NICKNAME WAS INSPIRED BY VOICE ACTOR PHILLIP GLASSER.

Phillip Glasser, who was seven years old when he worked on An American Tail, recalled that his grandmother would remind him to work on his lines every day when she dropped him off at the studio for work. "Hey Philly," she would say in a thick Bronx accent, "Time to learn your lines." Bluth overheard their exchange one day and loved it so much that he worked it into the movie—a mouse named Tony Toponi gives him the nickname "Filly."

Glasser is producing these days; here he is talking about his 2015 film, Life on the Line:

4. HENRI THE PIGEON WAS ORIGINALLY A SCRUFFY BIRD NAMED BOBO.

In early storyboards, the avian character was intended to look a bit scraggly and rough around the edges. When Christopher Plummer was cast instead, Henri was reimagined as the smooth, polished pigeon we know and love today.

5. STEVEN SPIELBERG WAS ACCUSED OF PLAGIARISM.

Throughout the late 1970s, artist Art Spiegelman had been developing a concept for a graphic novel he called Maus—a story that depicted Jewish people as mice and Germans as cats. He believed that Bluth and Spielberg had stolen the idea for An American Tail from him, but instead of suing, Spiegelman rushed to release the first half of his book before the movie came out to prove that he wasn't the plagiarist.

6. FIEVEL WAS THE SPOKESMOUSE FOR UNICEF.

Because "His immigration experiences reflect the adventures and triumphs of all cultures and their children," Fievel was announced as UNICEF's spokesmouse in 2000.

7. DREAMWORKS MAY NOT HAVE EXISTED WITHOUT IT.

An American Tail was jointly produced by Bluth's Sullivan Bluth Studios and Spielberg's Amblin Entertainment. The success of the movie, along with that of The Land Before Time, spurred Spielberg to open an animation branch of the business called Amblimation. The company made just three movies before Spielberg, Jeffrey Katzenberg, and David Geffen formed DreamWorks—and most of the Amblimation employees were brought over as the "main source feeding DreamWorks' animation division." The first movie they tackled was The Prince of Egypt.

8. WRITER DAVID KIRSCHNER IS ALSO RESPONSIBLE FOR ANOTHER POPULAR CHARACTER.

Before he was a writer, David Kirschner was a doll designer. That skill paid off a couple of years after An American Tail, when he designed another character that has its own place in pop culture, though a much different one than Fievel: Chucky, the homicidal doll from Child's Play.

9. SISKEL AND EBERT DID NOT APPROVE.

Gene Siskel and Roger Ebert gave An American Tail two thumbs down—with Ebert declaring, "This is the most downbeat movie since Return to Oz, which began, you may remember, with Dorothy being strapped down for electroshock therapy." Other critics tended to agree, but judging by the box office numbers, the public did not. The "downbeat movie" made more than $47 million domestically, beating Disney's The Great Mouse Detective, another mouse-centric animated film that had been released a few months earlier.

10. THE SCREENWRITERS HAD SESAME STREET BACKGROUNDS.

There's probably a reason An American Tail resonated with children, despite the serious subject matter: Thanks to decades of working on Sesame Street, the screenwriters knew how to talk to kids.

Screenplay writer Judy Freudberg was a longtime Sesame Street resident with 35 years under her belt. Freudberg joined the show as an assistant in the music department and ended up as a writer. Fellow screenwriter Tony Geiss also wrote for Sesame Street, including "Don't Eat the Pictures."

11. NO ONE EXPECTED "SOMEWHERE OUT THERE" TO DO SO WELL.

Songwriting team Cynthia Weil and Barry Mann were given four weeks to write four songs for the movie with James Horner. They didn't think they had written a hit, but after Spielberg listened, he was convinced that "Somewhere Out There" could be a Top 40 hit. He was right—the Linda Ronstadt and James Ingram duet peaked at #2 on the charts and won two Grammy Awards. It was also nominated for an Oscar, but lost to "Take My Breath Away" from Top Gun.

12. THERE WERE THREE MORE MOVIES.

Most people know that there was a sequel to An American Tail, in which Fievel and pals head West to seek their fortunes. But there were two more movies after that. An American Tail: The Treasure of Manhattan Island and An American Tail: The Mystery of the Night Monster came out in 1998 and 1999, respectively, and went straight to video.