To his friends, Peter Cullen is just a cowboy, a guy who loves horses (particularly American Quarter Horses) and the relaxed atmosphere of his California ranch, and who regularly invites a friendly group of rodeo riders over for some fun. But for an entire generation of children, Mr. Cullen is a hidden celebrity, a staple of their after-school and Saturday morning entertainment diet. And for the millions of die-hard “Transformers” fans who can barely contain their excitement over next week’s big-budget, live-action blockbuster, Mr. Cullen is nothing short of an icon. He is the pulse of a franchise that has become one of this summer’s most unlikely anchors — backed by Steven Spielberg, directed by Michael Bay, and riding a wave of excitement generated by an online trailer that has stirred millions of 20- and 30-something memories.

Ask your average New Yorker on the street about what they think of Peter Cullen’s work, and you won’t get an answer. But ask them about the animated characters Mr. Cullen has given life to in such franchises as “Winnie the Pooh,” “Gremlins,” “Predator,” and “Transformers,” and they may be surprised to learn that they have, in fact, been a longtime fan without even knowing it.

For some 30 years, Mr. Cullen, a native of Montreal, has made his voice into a comfortable career, jumping from cartoon series to cartoon series, feature film to feature film, as one of Hollywood’s most respected vocal talents. But it was his turn as Optimus Prime — the heroic, shape-shifting semi truck who stands for all that’s good and just about the Autobots — in the 1980s TV series “Transformers” that would mark a turning point in Mr. Cullen’s life.

“I was privy to all of this years ago,” Mr. Cullen said recently from Los Angeles, when asked if he was surprised that online fans not only knew his name, but were cheering his involvement in Mr. Bay’s blockbuster. “Years ago I had the fortunate good luck of taking my daughter’s advice and going to a “Transformers” convention. I remember saying to her: ‘Are you serious?’ and she said, ‘You have no idea how much kids I go to school with revere you.’ And then you go to this convention, and quite frankly I was utterly surprised and overwhelmed.”

Now, two decades removed from the last “Transformers” movie (an animated production resembling the original TV program), the news that Mr. Cullen would reprise the character he has voiced since its inception brought waves of elation from “Transformers” fans around the world. Indeed, when Mr. Bay was casting the voices for his film and A-list names such as George Clooney were raised as candidates to voice Optimus Prime, an Internet army virtually demanded that the director hire Mr. Cullen instead.

Generations of fans have come to love Eeyore in “Winnie the Pooh,” Mogwai in “Gremlins,” and even the strange, supernatural sounds of the Predator in the 1987 action blockbuster — all of which are to be found on Mr. Cullen’s lengthy resume — but it was the character of Optimus Prime that made him a hero to millions of children.

“I never thought it would be this big,” Mr. Cullen said not only of the “Transformers” movie, but of the original animated series that made its debut in 1984 and has continued to thrive on video, DVD, and online. “I thought it was all about a toy company that wanted to capitalize on having a show, but what do I know? Here we are, still talking about it.”

Despite the wave of public support for his participation, it wasn’t exactly a given that Mr. Cullen would make the cut for the film. Not present in the cast is Frank Welker, who originally gave voice to Optimus Prime’s archenemy, Megatron, and whose exclusion from the film has led to an outcry from “Transformers” purists. (Hugo Weaving, of “The Matrix” fame, will be voicing the character instead.)

So why was Mr. Cullen chosen for the film, but not Mr. Welker? Chalk it up to hero worship.

“It was the fans’ tenacity and their overall steady support that landed me the part,” he said. “I think their groundswell motivated the upper echelon [at Paramount and Dream-Works] to take a serious look at me,” Mr. Cullen said, aware that high-profile voice work in animated and computer-generated films has become the domain of major stars nowadays. “The fact that studios recruit high-profile voices and recognizable names, I’m not so sure in the long run that it’s necessary, because kids don’t know who the voice is when they’re watching animation. In my case, they didn’t even know what I look like, but they knew my voice. That original generation of fans will be more excited to hear me and recall all those original memories of Optimus Prime than if it was the voice of some celebrity. God love ’em.”

He’s also quick to concede that the studio saved quite a few pennies by hiring him. Mike Myers, for example, has earned more than $23 million as the voice of Shrek. Mr. Cullen said he drew a slightly more modest fee: “Oh, I’m nowhere near six figures! I was paid for five days of recording, and I think I could maybe buy a Toyota Corolla. Actually, I take that back, maybe a Solara. I could probably get a Solara.”

Not that he did it for the money. From the moment he stepped into his sound booth for the “Transformers” movie (quite a surreal sensation, he said, since the original series required all 13 actors to record their parts in a room together), Mr. Cullen said the surprising joy of the series came flooding back. And then he saw the updated, liveaction rendering of his character on a screen in front of him, as Mr. Bay’s digital Optimus Prime came to life.

“This is fun work, you better believe it,” Mr. Cullen said, recalling some favorite memories from his lengthy career. One particular highlight, he said, involved the sound he designed for “Predator,” the clicking sound that doubles as the alien’s language. “I was mostly trying to think of a sound that wouldn’t hurt my voice, and so I remembered from my childhood the sound of an upside down horseshoe crab while it was dying on the beach, the clicking sound of the air coming out of the body. And that clicking ended up working, and they ended up hiring me.”

As for “Transformers,” he was willing to dish out one spoiler, just from one fan to another, that suggests he’ll be back on the big screen very soon. It seems the producers of “Transformers” remembered that when Optimus Prime was killed at the end of the 1986 animated film, thousands of devastated fans decried the injustice. “I don’t even die in this one,” Mr. Cullen said. “They killed me off in the 1986 movie, but not this time. Hopefully that means I did an okay job.”

ssnyder@nysun.com