Peter Cullen, the legendary voice actor best known for playing Optimus Prime in the 'Transformers' franchise, has passed away. However, his final role as Thaedus in the animated series 'Invincible' will live on, bringing gravity and depth to the character.

The collaboration between Cullen and creator Robert Kirkman was a significant one for both parties. Kirkman has spoken about how working with Cullen was a test of his professionalism and how he handled lines from Cullen's iconic voice, Optimus Prime. For related coverage, explore our detailed analysis on Technology and Digital Systems.

Collaboration with Robert Kirkman

So to have him voicing the character he voices — it's crazy to have written dialogue that's coming out of his mouth," he added.

Cullen voiced Thaedus again in "Invincible" Season 4, released in 2026, making the Prime Video series his final credited project before his death in August.

Legendary voice actor Peter Cullen passed away on Wednesday, August 26, 2026 , leaving behind a long list of memorable characters. He was best known for playing Optimus Prime in the "Transformers" franchise across animated shows, live-action movies, and video games.

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But his final role was in one of the best superhero TV shows of all time : "Invincible." The animated Prime Video series follows Mark Grayson (Steven Yeun), who develops super strength and the ability to fly thanks to his alien father, Nolan, aka Omni-Man (J.K. Simmons).

However, after a game-changing twist, Omni-Man is revealed as a villain sent Mark later joins forces with the Coalition of Planets, a galactic alliance led Thaedus is introduced during Season 2 and becomes a key player in the fight against the Viltrum Empire. Cullen uses a deep, booming voice for the character, fitting Thaedus' role as the Coalition's leader.

Peter Cullens Final Details and Timeline

"Transformers" was a formative franchise for "Invincible" creator Robert Kirkman, which made collaborating with Peter Cullen especially meaningful. "Working with Peter Cullen was a huge test for my professionalism," Kirkman informed Polygon . "Just flat-out, every fiber of my being was screaming, 'Don't ask him about Optimus Prime ...

Just be a professional, come on.'" He explained that the show recorded lines with the cast over Zoom, and he kept his camera off during these sessions. Kirkman stated he was grateful for the decision because he was getting teary-eyed. "I've been hearing Peter Cullen's voice since I was like 7 years old.

So to have him voicing the character he voices — it's crazy to have written dialogue that's coming out of his mouth," he added.