Who voiced Optimus Prime in the 1980s Transformers animated series?

The answer is: Peter Cullen. Peter Cullen was the first actor to give a voice to Optimus Prime, the leader of the Autobots on the original Transformers animated series. Cullen got his first big break as an announcer on The Sonny & Cher Comedy Hour in the early ‘70s. Other voice actors have played Optimus Prime over the years, but Cullen reprised the role for the live-action films. Source