Transformers icon Peter Cullen died from cardiac arrest, death certificate reveals

The official cause of death for legendary voice actor Peter Cullen has been revealed, following his passing late last month at the age of 85.

The Canadian-born performer, whose deep and commanding baritone defined Autobot leader Optimus Prime across 40 years of the Transformers franchise, died on August 26 at his home in Los Angeles, a representative previously confirmed.

According to Cullen's death certificate, obtained by PEOPLE on Wednesday after TMZ first reported the news, the voice icon died from sudden cardiac arrest.

The official medical document lists respiratory arrest as an immediate underlying cause of death.

It further cites several significant secondary health conditions that contributed to his passing, including cerebellar metastasis—indicating cancer that had spread to the cerebellum part of the brain—along with hypoxia, chronic obstructive pulmonary disease (COPD), hypertension, and hyperlipidemia.

Cullen sadly died at his home in Los Angeles last week (Paul Archuleta/FilmMagic)

Cullen's passing marks the end of an era for television and cinema voice acting.

He first entered the pop culture history books in 1984 when he was cast as the voice of Optimus Prime for the original animated series The Transformers. Cullen famously based the character’s calm, steady, and noble cadence on his older brother Larry, a decorated US Marine Corps captain who served in the Vietnam War. His brother had advised him before his audition to play a hero who was "strong enough to be gentle" rather than loud and aggressive—a piece of advice that ultimately defined the moral core of the character.

Cullen went on to reprise the role across four decades, voicing Optimus Prime in the 1986 animated feature The Transformers: The Movie, before returning to headline director Michael Bay's blockbuster live-action film series starting in 2007. He continued lending his voice to the Autobot leader in modern franchise installments, including Bumblebee (2018) and Transformers: Rise of the Beasts (2023).

He was best know for voicing Optimus Prime and Eeyore. (Eric Charbonneau/WireImage for Paramount Pictures - CA)

Beyond his legendary work in the sci-fi franchise, Cullen was deeply beloved by Disney audiences for voicing the gloomy, lovable donkey Eeyore in The New Adventures of Winnie the Pooh and various spin-off films.

His extensive resume also included voicing Monterey Jack in Chip 'n Dale: Rescue Rangers and providing the terrifying, guttural vocal clicks and roars for the alien hunter in the 1987 action classic Predator.

Following the confirmation of his passing, tributes have flooded in from colleagues, voice actors, and generations of fans celebrating a performer whose voice anchored the childhoods of millions worldwide.