Batman #86 September 1966 -- "Batman Indian Chief."
Batman and Robin are on their way back to Gotham City when they spot a smoke bat-signals and a kid who looks just like Robin on horseback in a nearby field. The Dynamic Duo descend to investigate and they come upon a duo dressing like the Indian version of Batman and Robin. They introduce themselves as Chief Man-of-the-Bats, whose real name is Great Eagle and his young sidekick, Little Raven.
They inform Batman that they became the local heroes after being inspired by Batman and Robin's amazing adventures in Gotham City, but there is a downside to their presence. A man called Black Elk has become suspicious about Great Eagle being the Man-of-the-Bats and he has found a way to prove the truth. Without delay, Batman and Robin offer their help and play the roles of Man-of-the-Bats and Little Raven in order to throw off the attention from the Indian Chief and his son.