The song that launched Elvis’s career, “That’s All Right” was originally composed by Arthur Crudup on the bones of earlier blues music, and wasn’t particularly successful for his own career (he actually did another song that was basically the same thing just to get a little more mileage out of it).
It’s become somewhat popular in recent years to claim Elvis simply ripped off black performers, but the counterargument is that his willingness to sing their songs made it widely acceptable to appreciate them. Either way, great music was happening.