For more than 40 years, Peter Cullen’s voice made Optimus Prime sound unlike almost any other hero.

It was deep without constantly being aggressive. Commanding without sounding arrogant. Even when Optimus was preparing the Autobots for battle, there was usually a calmness underneath the authority.

Generations of Transformers fans came to recognize that voice almost instantly.

But Cullen did not create it by standing in an audition booth and asking himself what a giant alien robot should sound like.

He was thinking about one specific person.

His older brother, Larry.

Before Cullen auditioned for The Transformers in 1984, Larry — a Marine veteran who had served in Vietnam — gave him a piece of advice about what a real hero should sound like.

Cullen listened.

Then he walked into the audition and, by his own account, essentially performed an impression of his brother.

That decision helped create one of the most recognizable voices in popular culture.

Cullen Was Told He Was Auditioning for a ‘Hero Truck’

At the time, Cullen had no way of knowing what Transformers would eventually become.

The franchise was only beginning.

Cullen had already built a career as a versatile voice performer, but Optimus Prime was not yet an icon. He was simply another character Cullen was being asked to audition for.

Years later, Cullen recalled the circumstances during an NPR interview.

He had been told that the character was a hero.

He had also been told that the character was a truck.

Cullen was living with Larry at the time, and before leaving for the audition, he mentioned the unusual assignment to his brother.

He was going to audition to play a heroic truck.

Larry’s response would shape the character for decades.

Instead of encouraging Peter to make the performance bigger, louder or more traditionally heroic, Larry warned him against exactly that approach.

Don’t play the stereotypical Hollywood hero, he advised.

Don’t rely on shouting and exaggerated toughness.

Instead, Larry gave him the phrase that would become inseparable from Cullen’s understanding of Optimus Prime:

“Be strong enough to be gentle.”

Larry Cullen Knew Something About Real Strength

The advice carried weight because Larry was not talking about heroism as an abstract acting exercise.

He had served as a Marine in Vietnam.

Cullen remembered his brother as physically imposing but also compassionate, honest and controlled.

That combination mattered.

Larry did not believe strength required constant displays of aggression.

To him, a genuine hero could possess enormous power without needing to prove it every moment.

That became Peter Cullen’s blueprint.

When he entered the audition booth, he did not attempt to manufacture a futuristic robot voice.

He drew on Larry.

Cullen later summarized the process very simply: “I just did my brother, Larry.”

Suddenly, Optimus Prime had something much more important than a dramatic baritone.

He had a personality.

The Voice Worked Because Optimus Never Needed to Show Off

Listening to the original Optimus Prime after knowing that story changes the performance.

There is certainly power in Cullen’s delivery.

But Optimus rarely sounds like someone desperately trying to convince everyone around him that he is powerful.

He sounds certain.

That restraint separates him from countless booming action heroes and cartoon commanders.

Optimus can give an order without screaming it.

He can speak about sacrifice without turning the moment into a speech about himself.

And when he addresses the Autobots, the authority often comes from steadiness rather than intimidation.

Hasbro highlighted exactly that quality in its official remembrance of Cullen on August 27, 2026, crediting Larry’s advice with shaping a leader defined by dignity, compassion and self-sacrifice rather than posturing.

The company described Cullen’s six-decade career while emphasizing how deeply his performance influenced the way generations of viewers understood Optimus Prime.

That legacy took on even greater significance after Cullen’s death.

The actor died at his Los Angeles home on August 26, 2026, at age 85, surrounded by family, according to statements reported by multiple outlets.

Optimus Prime Became Much Bigger Than a 1984 Cartoon

Cullen first voiced the Autobot leader in the original Transformers animated series in the 1980s.

The franchise eventually expanded far beyond those television episodes.

There were additional animated productions, video games, toys and feature films. When Transformers was reinvented as a massive live-action movie franchise beginning in 2007, Cullen returned as the voice of Optimus.

Technology changed dramatically.

The animated robot of the 1980s became a towering photorealistic machine built with modern visual effects.

But the voice remained.

For longtime fans, Cullen’s presence created a direct connection between the childhood version of Optimus and the blockbuster incarnation decades later.

Cullen once described returning to the character as comfortably slipping back into something familiar. Optimus remained his favorite role, even after a career containing hundreds of voice credits.

And the voice still carried Larry Cullen inside it.

Cullen Also Gave Another Famous Character a Completely Different Voice

The remarkable thing about Peter Cullen was that Optimus Prime represented only one side of what he could do.

He was also widely known as the voice of Eeyore in numerous Winnie the Pooh productions.

The contrast could hardly be greater.

Optimus is a towering leader preparing to protect worlds.

Eeyore is a gloomy little donkey who seems perpetually surprised that anyone remembered he was there.

Cullen loved the reaction Eeyore could produce in children, and he ranked the character among his favorite roles after Optimus.

His career also included work connected to Knight Rider, The Predator, G.I. Joe and many other productions.

Yet Optimus became the performance most closely associated with his name.

Perhaps that was because Cullen never treated him simply as a robot.

The Real Man Hidden Inside Optimus Prime

Fans often talk about iconic voices as though they appeared fully formed from an actor’s imagination.

Cullen’s story is more personal.

When he needed to understand Optimus Prime, he did not study machines.

He remembered his brother.

He remembered a Marine who had experienced war but believed that strength and gentleness could exist together.

Then Peter Cullen took those qualities into an audition booth in 1984.

Four decades later, Hasbro was still repeating Larry’s advice while remembering the man who gave Optimus his voice. Cullen’s family even asked people honoring his legacy to lead others with compassion, integrity and loyalty while remembering that same idea about being strong enough to remain gentle.

Millions of people thought they were hearing the perfect voice for a heroic robot.

Peter Cullen knew differently.

They were hearing his big brother.