LOS ANGELES, Aug. 29 -- Before Peter Cullen ever said a word as Optimus Prime, he went home to think about his brother.

It was 1984. Cullen had an audition for a new animated series called Transformers, and the producers wanted a leader, a robot in disguise who commanded authority without arrogance. Cullen thought of Larry, his brother, a United States Marine Corps veteran who came back from Vietnam carrying the weight of what he had seen but never surrendered his gentleness. "Be strong enough to be gentle," Cullen later said Larry had taught him. He walked into that audition, and Optimus Prime was born.

Cullen died Wednesday at his home in Los Angeles. He was 85. His family confirmed the news in a statement, NBC Los Angeles reported. N...