Spoiler alert! We're discussing important plot points and the ending of "Transformers One" (in theaters now), so beware if you haven't seen it yet.

Optimus Prime transforming into a truck and rolling out with his Autobots is an image seared into anybody’s brain who watched the old 1980s “Transformers” cartoons or the more recent live-action movies.

So it’s an amusing sight in the animated origin story “Transformers One” when Optimus – or Orion Pax (voiced by Chris Hemsworth), as his younger self is known – and his robot friends first get their transforming cogs and have difficulties. Mechanical heads go back in when they shouldn’t and limbs don't work as they try and switch to new vehicle modes.

That’s a moment straight out of director Josh Cooley’s toy box.

“One of my memories of having Transformers was some of them were too complex to actually work. You get about halfway and go, ‘I can't figure this out. Dad, help me!’ ” says Cooley (“Toy Story 4”). “Most of my childhood, the Transformers were kind of half done on the floor.”

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Raised on “Transformers” Saturday morning cartoons, Cooley included a bunch of Easter eggs and references in “Transformers,” which chronicles the story of how Optimus and Decepticon rival Megatron – aka D-16 (Brian Tyree Henry) – went from best friends to mortal enemies. Here, the filmmaker breaks down the ending, the best cameos and a consequential post-credits scene:

What happens in the ending of ‘Transformers One’?

With their friends Elita-1 (Scarlett Johansson) and B-127 (Keegan-Michael Key) – best known as fan favorite Bumblebee – Orion and D-16 go on a mission to find the mythical Matrix of Leadership but discover that their leader, Sentinel Prime (Jon Hamm), sold out their home world of Cybertron to the evil Quintessons and was responsible for the deaths of the ruling Primes. Orion wants to hold him accountable, while the angry D-16 wants him killed. During their revolution, D-16 accidentally shoots Orion while aiming for Sentinel, and instead of saving him, lets him fall into the planet’s core. But that turns out to be where the Matrix is: He’s revived by the Primes, turned into the mighty Optimus and defeats his former BFF, exiling him and his new followers.

Cooley first considered an ending that didn’t have them battle it out in epic fashion, but “you want that,” he says. “When (Megatron's) gun comes out, that's a moment. When (Optimus') mask comes up, that's a moment. Those are the things that you're leaning in waiting for.”

Are there any old-school 'Transformers' cameos?

Fans of the ‘80s cartoon series will see a lot of familiar faces. Certain characters, like the Autobots’ Jazz and Decepticon mainstays Soundwave, Shockwave and Starscream (the latter played by Steve Buscemi), have significant scenes while many others are name-checked or seen in the background for eagle-eyed viewers. At one point, Cooley realized animators “were sneaking characters into the shots that were their favorites,” he recalls. “I said, ‘You know what? Keep doing it.’ ”

Cooley even cast himself in one role, voicing the Decepticon jet Skywarp. “Decepticons are so much fun,” the director says. “It was an opportunity to play like I'm a kid again, honestly.”

Does ‘Transformers One’ have a post-credits scene?

It actually has two extra scenes. One comes after the first chunk of credits, where B-127 proudly shows his laser-y “knife hands” to the piles of junk he considers his “friends” – and accidentally slices off one of their “heads.” The other comes right before the theater lights come up: Megatron brands all of his new followers with the familiar Decepticon sigil and gets them riled. “We will not be blinded by his deception,” he says of his old pal. “Decepticons, rise up!”

“We knew it was important for him to call them Decepticons at some point,” Cooley says, and the original plan was to have that moment before the climactic battle. It felt “shoehorned” into the narrative there, so Cooley decided to give it a special place at the very end of the movie, which was “kind of awesome.”

It also gives a reasoning behind the villainous faction’s name, Cooley adds. “Nobody would go out and go, ‘We’re the bad guys!’ Giving (Megatron) his own kind of evil Optimus speech at the end, there was a way for him to be like, ‘We were screwed over and we're not going to be the ones that are going to be taken for granted anymore. We're going to own it.’ ”