Fearsome in the ring, George Foreman was so charming outside it he became America’s favorite pitchman. The Olympic gold medalist and two-time world heavyweight boxing champion fought the sport’s legends, helping define boxing’s golden era alongside Muhammad Ali and Joe Frazier in the 1970s. After saying he’d seen a holy vision, he quit the sport in 1977 to become a preacher and open a youth center in Houston. But he managed an improbable comeback a decade later. Despite widespread skepticism that he could even get back into shape...