‘Transformers’ Voice Actor Peter Cullen’s Cause of Death Revealed a Week After His Passing

Optimus Prime’s booming, principled voice became a defining sound of childhood for generations of fans, first through Saturday morning cartoons and later through a string of blockbuster films. Few voice actors have left as lasting an imprint on a single character as the man behind that iconic Autobot leader.

Peter Cullen died on August 26 at his home in the Toluca Lake neighborhood of Los Angeles at the age of 85. His agent, Kevin Motley, confirmed the news at the time, and Cullen’s family described his passing as peaceful, surrounded by loved ones, while his fans mourned the loss of a voice that had shaped so much of their favorite childhood entertainment.

Now, roughly a week after his death was first announced, the cause has been made public. According to a death certificate obtained by TMZ, Cullen died of cardiac arrest brought on by respiratory arrest, with a malignant neoplasm of the lower lobe of the lungs listed as the underlying cause.

The official documentation also revealed several additional health complications that contributed to Cullen’s decline. Court records cited by PEOPLE noted secondary conditions including cerebellar metastasis, indicating that the cancer had spread to the cerebellum, along with hypoxia, chronic obstructive pulmonary disease, hypertension, and hyperlipidemia.

That combination of conditions paints a picture of a prolonged and serious health struggle in the time leading up to Cullen’s death, even as his family kept those details private during his final months. Cullen is scheduled to be buried at Forest Lawn on September 9, giving fans and colleagues a chance to formally honor his legacy.

In their original statement following his passing, Cullen’s family reflected on how they wanted him to be remembered. “Peter Cullen passed away peacefully, surrounded by his loving family, and held in the hearts of his many friends and countless fans worldwide,” the family said, according to TMZ. They added a request that fans “honor his remarkable legacy by serving your communities and leading others with compassion, integrity, and loyalty and always remember ‘be strong enough to be gentle.'”

Cullen first stepped into the role of Optimus Prime in the original 1980s “Transformers” animated series, establishing a commanding yet compassionate tone that became inseparable from the character. He went on to reprise the role across Michael Bay’s live-action film franchise, along with numerous animated series and video games spanning more than four decades.

His work extended well beyond the Transformers universe as well. Cullen was also widely beloved for voicing the gloomy donkey Eeyore across various Winnie the Pooh projects, in addition to voicing Monterey Jack in “Chip ‘n Dale: Rescue Rangers” and providing the guttural vocal effects for the alien hunter in 1987’s “Predator.”

In a fitting final chapter, Hasbro confirmed that Cullen had recorded one last performance as Optimus Prime before his passing, for a short titled “Optimus Prime: Awakening,” set to accompany the 40th-anniversary theatrical re-release of “The Transformers: The Movie.” Frank Welker, who returns as Megatron and Soundwave opposite Cullen’s final performance, reflected on their decades-long collaboration, saying Cullen’s portrayal of Prime was rooted in his own personal values of honesty and loyalty, and that those qualities made their friendship an easy one.

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