When Brad Bird's feature directorial debut arrived in theaters on August 6, 1999, the film was a critical success. But due to misdirected marketing from Warner Bros., that positive reception didn't carry over into the box office. The Iron Giant would have to wait until the next millennium to achieve its cult status as a modern animated classic. Here are 10 facts worth knowing about the beloved cartoon.

1. The Iron Giant is based on a Ted Hughes novel.

Nine-year-old Hogarth Hughes—and his mother, Annie Hughes—both share a name with the British Poet Laureate who wrote the children’s book the film is based on. Published in 1968, Ted Hughes penned The Iron Man to comfort his children after the suicide of his wife, Sylvia Plath.

The novel tells the story of a mysterious metal monster who befriends a young boy and becomes the world’s most unlikely hero, but its similarities to the film end there. When Hogarth first encounters the Iron Man in the book, he tricks him by leading him to a covered pit and burying him alive. The robot remains buried for months, eventually digging himself out in time to save the planet from an extraterrestrial invader dubbed the "Space-Bat-Angel-Dragon." The alien later reveals that it had been drawn to the planet by the warfare it witnessed there. The Iron Giant’s anti-war sentiments are slightly more straightforward, with the Giant (*spoiler alert*) protecting the world from a nuclear bomb instead of an interstellar dragon.

2. Hughes praised The Iron Giant's screenplay.

Sadly, Hughes passed away a year before the movie was released. He did, however, live long enough to read the script. Despite its departure from the source material, Hughes was impressed. He expressed his approval in a letter to the studio: "I want to tell you how much I like what Brad Bird has done … He’s made a terrific dramatic situation out of the way he’s developed The Iron Giant. I can’t stop thinking about it."

3. The Iron Giant was originally meant to be a Pete Townshend musical.

Before The Iron Man was reimagined as an animated children’s film, it was adapted by The Who guitarist Pete Townshend into a solo concept album of the same name. The 1989 rock opera feature such tracks as "Man Machines," "A Friend Is A Friend," and "I Eat Heavy Metal." In the early 1990s, Townshend relaunched his musical concept as an onstage production. This attracted the attention of Warner Bros., and the studio secured the rights with the intention of turning it into an animated musical.

But Townshend’s rock opera vision never did make it onto the big screen. After Bird signed on to direct, he scrapped the musical numbers and reworked the script, further removing the story from both the rock album and the children’s book upon which it was based. Townshend remained credited as an executive producer, and after seeing the movie he reportedly commented, "Well, whatever, I got paid."

4. The Iron Giant marked Brad Bird's feature directorial debut.

As the director of two beloved Pixar films, The Incredibles (2004) and Ratatouille (2007), Bird—a two-time Oscar winner—is considered one of the most respected figures in the animation biz. But it was The Iron Giant that proved his directing chops and instinct for story to the Pixar team.

Before directing his first feature for Warner Bros. animation, Bird got his start at Disney. He sent an animated short to the studio and Disney legend Milt Kahl was so impressed that he took on a teenaged Bird as his protégé. His first animation job was working on The Fox and the Hound (1981), and a few years later he was offered his first shot at writing and directing for the Steven Spielberg series Amazing Stories. Bird really began to receive recognition in the industry after joining The Simpsons. He directed the classic episode “Krusty Gets Busted," which paved the way for him to direct his first feature. For a while that was shaping up to be Ray Gunn, a retro-futuristic film noir inspired by a misunderstanding of a B-52s lyric. He was developing the script for Turner when the studio merged with Warner Bros., and they transferred him to work on an in-development project called The Iron Giant instead.

5. The Iron Giant's title character was computer generated.

Despite being considered one of America’s last great traditionally animated films, The Iron Giant’s title character was created entirely with a computer. The creators took careful steps to make sure the Giant blended in seamlessly with the hand-drawn world. They even went so far as to develop a computer program to make the character’s lines wobble slightly, producing a crude, hand-drawn effect.

6. The Iron Giant features a pre-Fast and Furious Vin Diesel.

Before making a name for himself as an action star, Vin Diesel provided his voice to the towering robot in The Iron Giant. Not counting groans and grunts, the Giant utters a grand total of 53 words in the entire film. When Diesel returned to feature voice acting 15 years later for Guardians of the Galaxy, he played Groot—a character whose vocabulary is even more severely limited.

7. The Iron Giant's design was inspired by the art of Normal Rockwell.

The Iron Giant takes place in an idyllic Maine town in the 1950s—a perfect contrast to the themes of McCarthy-era paranoia the film explores. To give the setting more of a wholesome, Americana look, the creators drew inspiration from the art of Edward Hopper, N.C. Wyeth, and Norman Rockwell. Even the fictional town’s name—Rockwell—is a nod to the iconic American artist.

8. Brad Bird rejected the comparisons to E.T.

It’s easy to see how a movie about a misunderstood boy who befriends a visitor from outer space, hides him from the government, then says a tearful goodbye following a climactic aerial chase scene would draw comparisons to Steven Spielberg's E.T. CNN’s review mentions the "charming E.T.-like friendship between the boy and the intimidating but apparently benign metal giant," while Roger Ebert said, "Imagine E.T. as a towering metal man, and you have some of the appeal of The Iron Giant." While these comments aren’t exactly negative, Bird apparently didn’t find the comparisons too flattering. He told Salon, "E.T. doesn't go kicking ass. He doesn't make the Army pay. Certainly you risk having your hip credentials taken away if you want to evoke anything sad or genuinely heartfelt."

9. The Iron Giant includes cameos from two Disney animators.

Though the film was produced by Disney’s historic rival Warner Bros., Bird managed to slip in cameos from two of the studio’s greatest animators. The train workers Kent interviews at the train crash scene are voiced by and modeled after Frank Thomas and Ollie Johnston, two of Bird’s mentors during his early years at Disney. They also make an appearance at the end of The Incredibles.

10. The Iron Giant gained a cult following after it left theaters.

By the time Warner Bros. realized they had something special on their hands with The Iron Giant, it already was too late. The film was criminally under-marketed and performed poorly at the box office as a result. The studio had learned its lesson when it came time to promote the movie’s home video release. They partnered with big-name brands like General Motors, Honey Nut Cheerios, and AOL, and even distributed $2 off coupons at screenings of Pokémon: The First Movie. Then in 2000, the rights to the film were sold to Cartoon Network and TNT. Cartoon Network started airing Iron Giant marathons on Independence Day and Thanksgiving, and as more children (and adults) were introduced to the film it eventually gained a devoted fan base.