Chief Thunder-Cloud as Tonto, and Lee Powell as The Lone Ranger, from the 12-part Republic serial The Lone Ranger (1938).
Powell was dubbed over as the Lone Ranger by Bill Bletcher, and Earle Graser when crying out "Hi-Yo, Silver!" Bletcher had done extensive voice work in animation, and Graser had been the original radio Lone Ranger.
This was done because part of the plot of the serial is that the villain is trying to figure out which of five characters could really be the Lone Ranger. The studio wanted this to be a mystery to both the bad guy and the audience until the very end, so they didn't want anyone recognizing Powell's voice under the mask.
Republic would revisit the same gimmick in 1943 with The Masked Marvel serial. Not only was the Masked Marvel dubbed while in costume, Republic went one step further when his identity is revealed at the end: the actor playing the Marvel's alter ego was nowhere near the same size or build of the stuntman who played the hero.