Some great singers never took a days music class in their lives. However... many of these same singers have had surgery on their throats because they never learned to sing properly. They never learned to breathe or how not to strain their voice.
I can't tell you for certain if any of your favourites have had any training or not, but what I can tell you is... that not one of them started out singing the way they sounded when they started recording. Why..
Because everyones voice changes (not just men), we go from mimicking our favourites to finding new singers to emulate. Eventually you'll find you're own style. And then you'll find your voice, like the three men above.