This is the real-life family tragedy that inspired 'The Iron Giant'

Brad Bird started off his career as an animator, working on The Black Cauldron and The Fox and the Hound, and was even a director and executive consultant on The Simpsons during its golden years. He later stepped up to take on the role of director and writer later on, helming Pixar movies Ratatouilles and The Incredibles.

Now he's one of Hollywood's biggest directors after lending his talents to live-action movies Mission: Impossible - Ghost Protocol and Tomorrowland, and returning to animation to make The Incredibles 2 this year. But for me, and for many others, his best movie will always be 1999's The Iron Giant - which he wrote and directed, and even helped out with the animation on.

In the film, a colossal robot crash lands on Earth, bumping its head and losing its memory. The giant befriends local boy Hogarth, who hides it from the military, teaches it about the world, and keeps it from fulfilling its programmed mission: which is to destroy.

The Iron Giant didn't do too well at the box office, but went on to find an audience that appreciated it on DVD and television - and part of this came from its timeless use of anti-war, anti-violence, and even anti-gun messages.

However, it was later revealed that this message is connected to a very real tragedy in the director's life.

At the 2016 San Diego Comic-Con, Bird introduced a documentary titled 'The Giant's Dream: The Making of The Iron Giant', saying of the process, "It’s easy to forget what it was like to make […] because this was a moment in time that was very unique."

But it was what he said in the documentary that shocked and moved the audience, when he spoke about the death of his sister:

"My sister Susan, who I love very much and was very close to, died of gun violence.

"Pointlessly, she was killed by her husband. I was devastated.

"When you shoot somebody, you’re not just killing that person. You’re killing a part of all the people that love that person."

Susan was shot and killed by her estranged husband before the film's story was completed, motivating Bird to emphasis the anti-gun message of the film.

The Iron Giant features a machine programmed for violence, that becomes overwhelmed with a desire to destroy whenever he sees a weapon of any sort. However, he's taught that he has a choice to take another path - one of empathy and sacrifice.

Speaking to Spliced in 1999, Bird said:

"The idea I pitched to Warner Bros. after reading the book - when I said that I really liked it but I wanted to do something different with it - was I said 'What if a gun had a soul?'

"That kind of stuck with them."

It's a powerful idea, but the origins weren't widely publicised, with many not discovering this information until years later.

With Susan's tragic death in mind, certain moments from the movie stick out, from lines like as "souls don't die" to Hogarth's advice to his newfound gargantuan friend:

"It's bad to kill. Guns kill. And you don't have to be a gun. You are what you choose to be. You choose."

There's a reason that certain movies, like The Iron Giant, resonate so much with us. It's not just about the entertainment value, but the values they teach and the messages we can relate to. In Brad Bird's case, he was able to make a thrilling family movie that doubles up as a moving tribute to his lost loved one.