Vin Diesel may be an action star, but the Iron Giant and Groot are his magnum opus. (Warner Bros./Marvel Films)

Every Tuesday, Jeremy Fuster analyzes a critical scene from a popular film. Join him every week as he delves into what exactly makes these critical scenes so memorable and successful.

If there was one big takeaway from the 2014 summer blockbuster season, it was this: CGI characters are on the rise. While the top stars of years past were flesh-and-blood humans like Robert Downey, Jr. and Heath Ledger,  the ones that left the biggest impressions on moviegoers this time around came from mo-cap suits, voice acting, and top-of-the-line visual effects. Sure, not all of them were hits; but for every creepy, grungy-looking Ninja Turtle there was a jaw-dropping legion of apes whose nuanced expressions and movements made their struggle between war and peace uncomfortably human-like.

But the kings of this new wave of computerized creatures have to be Rocket Raccoon and Groot, two-fifths of the most charming superhero team ever seen on film, the 'Guardians Of The Galaxy.'

Now, the fact that these two characters are a smartass raccoon and a giant walking tree with superhuman strength makes them pretty easy to market to moviegoers. But director James Gunn wanted to do more than just make them some goofy spectacle. He wanted to show that this duo, like their fellow Guardians, had a bitter past filled with loss and suffering. To do this would require making the audience take seriously a talking animal and a plant who says one line over and over. How did they pull it off?

READ MORE: Film Review: 'Guardians Of The Galaxy'

A big part of reaching that goal, of course, was finding the right voice acting, and 'Guardians' hit a home run by casting Bradley Cooper as Rocket and Vin Diesel as Groot. This week and next, we will be looking at movies that influenced both actors' performances, starting with another film in Diesel's filmography: 'The Iron Giant.'

Diesel's job as Groot was simple on paper but difficult in execution. He had to say "I am Groot" in five different languages, but make each utterance of that line fit a different emotion or situation. But one of the reasons why Diesel was chosen to take on this challenge -- and why he was so up to it -- is because he was already famous for packing pathos into lines that are three words or less.

15 years ago, back when Diesel was just getting his career started, he got his first voice acting role in 'The Iron Giant' as the film's titular robot. 'The Iron Giant' has been widely regarded as one of the greatest animated films ever made and a cult classic, weaving a tale of a mysterious robot from outer space that crashes in New England and befriends a young boy named Hogarth. The Giant's true purpose is never explained, but it is highly implied that it would have had the power to easily destroy mankind had its first encounter with humans been more violent. Instead, Hogarth teaches the Giant not to kill, carving a message of nonviolence and heroism into the empty slate that is the Giant's mind.

To see this lesson and Diesel's minimalist acting chops on display, let's look at the scene where Hogarth tells the Giant what a soul is:

Much like Groot, the Giant isn't able to speak complete sentences. In fact, it is even implied through the way it repeats Hogarth's words that while the possibility of learning speech was built into it, interaction with humans was probably the lowest priority. Up to this point in the film, the Giant's speech conveys very little emotion. Its first words in the film even sound more like creaking metal than English.  But here, Diesel gives the Giant's words a growing sense of humanity as it comes to grips with the concept of death. The robotic grinding that the Giant once communicated with has given way to Diesel's deep, reverberating voice, one that clearly shows the Giant's confusion, sadness, and reflective thought.

READ MORE: Remember This Scene?: 'The Grand Budapest Hotel'

The parallels between Groot and the Giant are numerous and profound. Both are powerful, nearly indestructible beings limited to simplistic forms of communication. Both need much smaller creatures to protect and guide them. And, most importantly, both develop deep friendships over the course of their respective films, leading them to make the ultimate sacrifice for others. All of these qualities come alive through Diesel's deep, evocative voice, and while he may be known best as an action star, it is his ability to do so much with so little in these two movies that shows his true talent.

"Superman."

"We are Groot."

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