Early "Horse Whisperers":
"Daniel Sullivan (died 1810) from Mallow, Co. Cork, Ireland, was an Irish horse trainer, who specialised in rehabilitation of horses which were unresponsive to traditional methods. A large portion of his work took place in England.
Not very much is known about him, since he was secretive about his actual methods. To the people who were able to watch him at work, he appeared to frequently stand so close to the horse that they assumed he was whispering to it. For that reason he became known as the "horse whisperer." https://en.wikipedia.org/wiki/Daniel...er%22_Sullivan
"There was a man from Groveport, Ohio called John Solomon Rarey, who tamed his first horse at the age of twelve. Word of his gift spread and in 1858 he was summoned to Windsor Castle in England to calm a horse of Queen Victoria. The queen and her entourage watched astonished as Rarey put his hands on the animal and laid it down on the ground before them. Then he lay down beside it and rested his head on its hooves. The queen chuckled with delight and gave Rarey a hundred dollars. He was a modest, quiet man, but now he was famous and the press wanted more. The call went out to find the most ferocious horse in all England.
It was duly found.
He was a stallion by the name of Cruiser, once the fastest racehorse in the land. Now though, according to the account Annie read, he was a "fiend incarnate" and wore an eight-pound iron muzzle to stop him killing too many stableboys. His owners only kept him alive because they wanted to breed from him and to make him safe enough to do this, they planned to blind him.
Against all advice, Rarey let himself into the stable where no one else dared venture and shut the door. He emerged three hours later leading Cruiser, without his muzzle and gentle as a lamb. The owners were so impressed they gave him the horse. Rarey brought him back to Ohio, where Cruiser died on July 6, 1875, outliving his new master by a full nine years." John Solomon Rarey, the Original Horse Whisperer
Somehow, I doubt anyone was the "Original Horse Whisperer", or the first "natural" horseman.