Jeffrey Preston Bezos was 4 years old when he first arrived at his grandfather's cattle ranch in Cotulla, Texas. The Lazy G is a sprawling 25,000-acre spread in the southwest part of the state—an unspoiled habitat of mesquite and oak trees, the home of whitetail deer (popular among local hunters), wild turkeys, doves, quail, feral hogs and sheep.

Jeff's maternal grandfather, Lawrence Preston Gise, was a just-retired rocket scientist who was ready to trade in his missile research for the simple and demanding life at the ranch,...