The opening paragraph of Ted Hughes’s children’s book The Iron Man introduces its title character in a strange and contradictory way. Its entrance is pitched halfway between mythmaking and slapstick. No sooner has the giant metal figure descended upon the earth than an errant step sends him hurtling off the edge of a cliff: “His iron arms broke off, and the hands broke off the arms. His great iron ears fell off and his eyes fell out. His great iron head fell off. All the separate pieces tumbled, scattered, crashing, bumping, clanging, down on to the rocky beach far below.” He rebuilds himself, but Hughes has established his hero’s mix of power and vulnerability. The bigger they are, the harder they fall.

Published in 1968—the same year as Philip K. Dick’s seminal replicant thriller Do Androids Dream of Electric Sheep and the film versions of 2001: A Space Odyssey and Planet of the Apes—The Iron Man was not initially received as a science-fiction landmark. A modest fable about a Christ manqué robot didn’t register as a priority for critics. The book was popular, however, and, like its namesake, it’s come to cast a long shadow.

The premise of a massive mechanical creature moving through the English countryside was conceived under the sign of H.G. Wells’s War of the Worlds, updating its turn-of-the-century paranoia with a twist. Hughes’s visitor doesn’t need to be defeated, but embraced; it is taken in by a small boy, who helps to welcome it into a frightened but accepting human community. Their friendship rebuked the machine-vs.-man subtext of 2001 and anticipated the bonding rituals of everything from E.T. to Terminator 2: Judgment Day. Introduced as a potential threat, the Iron Man becomes humanity’s protector, a role that introduces an aspect of religious allegory and recontextualizes his earlier pratfall. We’re worried about him and counting on him at the same time.

Brad Bird’s movie adaptation is not particularly faithful to the plot of Hughes’s story, shifting the setting from the U.K. in the late 1960s to 1950s America, swapping out groovy Summer of Love vibes for Cold War paranoia, and jettisoning the book’s third act, which featured an intrusion by an extraterrestrial dragon that wanted to burn Earth to cinders. Nevertheless, The Iron Giant captures and crystallizes its source material’s anxious, humane spirit. It might be the most empathetic and exhilarating mainstream American animated feature ever made, a close cousin in form and feeling to the most sublime titles of Japan’s famed Studio Ghibli.

Bird, who had worked for Disney as an animator on The Fox and the Hound before making his name working on The Simpsons during its glory days, took on the project in the midst of personal tragedy. His sister Susan had been shot to death by her estranged husband, a horrific event that gave additional urgency to the director’s pitch to Warner Bros.: “What if a gun had a soul?” In Hughes’s book, the Iron Man shows his strength mostly by taking punishment, passively allowing the space dragon to singe and scald his steel exterior in a Christ-like gesture of turning the other cheek. In Bird’s version, the Iron Giant is a fully weaponized creation capable of laying waste to everything around him; the suspense lies in whether he will pull his own trigger.

It would be simplistic to reduce a film as rich and multileveled as The Iron Giant to a simplistic anti-NRA screed, however. In visual terms, it’s an astonishingly beautiful world, encoding the disparity between its cozy, homespun Maine setting and the mystery embodied by the Giant in a collision of animation styles. The human characters were hand-drawn, but the robot was rendered with the assistance of computer-generated imagery. There’s some of The Simpsons in Bird’s style, like a hilariously blunt “duck and cover” PSA that could have been hosted by Troy McClure, or the myriad humiliations suffered by nasty G-man Kent Mansley (voiced by Christopher McDonald), who has descended on a small town in Maine to locate what he suspects is a downed Russian satellite.

Mansley’s disparaging allusions to Sputnik set the action in 1957, while the name of the town where the Giant lands alludes more generally to the Eisenhower era as a whole: Rockwell. The Iron Giant came out in 1999, the same year as American Beauty, and its suburban satire is at once gentler and sharper than Sam Mendes’s Oscar winner. Rather than mocking or vilifying small-town values—or scoring sarcastic points via the distance between the story’s historical setting and his own enlightened 21st-century perspective—Bird filters authentic social, cultural, and technological history through the tropes of 1950s science fiction. Nine-year-old Hogarth Hughes (Eli Marienthal) devours comic books and monster movies, which prepare him for the Giant’s arrival without diminishing his sense of fear or wonder. When the boy and the robot meet in the forest for the first time, it’s a close encounter of the Spielbergian kind, awash in genuine awe.

The characters are beautifully designed in allegorical counterpoint to one another. The mostly mute, scarily imposing, and yet essentially innocent Giant (voiced by Vin Diesel) connotes post-Hiroshima technophobia, while Hogarth embodies the optimism generated by the space race—the hope for something better. Their tentative, fraternal relationship, which sees Hogarth assume the role of big brother despite his smaller stature, is at the heart of the film’s most emotional moments, like a forest idyll that ruthlessly evokes the death of Bambi’s mother (and leads to a deceptively naive disquisition on morality excellently explicated by Sam Adams here).

It’s the character of Dean (Harry Connick Jr.), a local beatnik who takes a liking to Hogarth and uses his junkyard to hide the Giant from Mansley, who represents the film’s conceptual masterstroke. Within the film’s 1950s schema, Dean represents countercultural dissent (“If we don’t stand up for the kooks, who will?”). As an artist who is also a moralist, he is recognizable as Bird’s stand-in, quietly guiding both of his friends toward their heroic destinies. “You don’t have to be a gun,” Hogarth pleads during the climax while the Giant is on violent autopilot. His words deactivate the robot’s combat protocol, but Hogarth absorbed the lesson from Dean and his earlier assertion about the importance of nonconformity: “You are who you choose to be.”

Critics have long speculated on the individualistic subtext of Bird’s work: In a thoughtful essay for The Atlantic, David Sims examined the idea that the director is a closet Randian objectivist, concluding that while Bird does indeed tend to fixate on characters who feel creatively stifled—from the would-be master chef Remy in Ratatouille to Tomorrowland’s self-exiling utopian engineers—they seek self-expression rather than domination over others.

I’ve never been fully comfortable with the conjoined persecution-superiority complexes established (and ultimately vindicated) for the paranormally empowered family of The Incredibles, which always seemed to me like a family-friendly riff on Watchmen, including a villain whose plan revolves around convincing society that costumed crusaders and their amazing abilities are the real enemy. Mr. Incredible feels unappreciated despite his accomplishments, while the Giant, who strongly identifies with a certain DC icon after Hogarth shows him his comic book collection, displays truly Kryptonian selflessness in the home stretch, intercepting a nuclear warhead aimed at Rockwell and taking Hogarth and Dean’s lesson about self-definition to heart.

It’s not enough to just not be a gun; the machine has a superhero’s soul. When Diesel (whose vocal performance here paved the way for Groot) leans into the Giant’s final three syllables, the rush of emotion and pop-cultural resonance is overwhelming.

If Bird had had the courage to let his hero’s self-sacrifice be the film’s true grace note, The Iron Giant would join the ranks of fully unsentimental end-of-childhood fantasies. But the director chose to end where Hughes began, inserting a coda in which the Giant is shown reassembling himself, ostensibly for future adventures. Hughes actually wrote a sequel—1993’s The Iron Woman—but Bird never planned on continuing the story, although the film’s commercial failure rendered such questions moot. The Matrix aside, the summer of 1999 was not a good stretch for Warner Bros., which botched the promotion of two idiosyncratic masterpieces one month apart (the other one being Eyes Wide Shut), but Bird has downplayed criticisms of the studio’s efforts. “Some of that was warranted,” he told Entertainment Weekly in 2016, “but to me, the most important thing was that they made the film. They made a kind of movie that really no one else was making.” That’s true enough, and so is the fact that nobody—including Bird himself—has really come close since.