Sorry, but I've got to give this to Georg. Hackenschmidt is essentially the first universally accepted World Heavyweight Champion in wrestling history. After defeating Tom Jenkins, who was the American Heavyweight Champion, in New York in 1905, Hackenschmidt was cemented as the first Undisputed World Champion in wrestling. Prior to that, he won almost every major wrestling title in Europe. He held the World Championship for nearly 3 years before losing to Frank Gotch.
The man was a legitimate athlete and tough guy and wrestled matches that were nothing more than shoots. Matches that would sometimes last hours on end. I'm sorry, but William Regal would be completely overmatched in every measurable way. I like Regal, I always have, but Hackenschmidt could outwrestle him and outpower him.