His Optimus Prime voice was inspired by his older brother, a decorated US Marine and Vietnam War veteran, who suggested he should play the character as “a real hero, don’t be a Hollywood hero”.

“He said, ‘Don’t go yelling and screaming. He’s strong enough to be gentle.’

“And that resonated with me, and I could hear his voice all the way to the audition. When he drops down, when he gets serious, is where I found Optimus Prime.”

Cullen gave his brother a cut of the wages he received for playing Optimus Prime until his death.

The actor’s performance as the character earned him a Daytime Emmy nomination for outstanding performer in an animated programme in 2011, and he was honoured with a lifetime achievement award at the Children’s & Family Emmy Awards in 2023.

Cullen’s other roles included Monterey Jack in Chip ‘n Dale Rescue Rangers, and he voiced characters in 1980s and 90s animated series including Spider-Man, Donkey Kong, Alvin & the Chipmunks, Dungeons & Dragons, My Little Pony, Duck Tales and Gummi Bears.