At 79, thomas starzl doesn't have much left to prove. In July 1967, the surgeon was the first to perform a successful human liver transplantation; since then he has been instrumental in making the liver the United States' second-most-commonly transplanted organ. "He led the field of transplantation into the modern era," says J. Richard Thistlethwaite, a transplant surgeon at the University of Chicago.

Select from the choices above to read the entire article.