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, and he wanted to share that life with his grandson. Until he was 16 years old, Jeff spent every summer there.

At the ranch he learned to clean stalls, to brand and castrate cattle, to install plumbing and to handle other ranch-hand tasks. One day, his grandfather towed in a dilapidated D6 Caterpillar bulldozer with a stripped transmission. Fixing it would be tough: He would have to remove a 500-pound gear from the engine. No problem; he simply built himself a small crane. Jeff helped.

"One of the things that you learn in a rural area like that is self-reliance," Mr. Bezos said. "People do everything themselves. That kind of self-reliance is something you can learn, and my grandfather was a huge role model for me: If something is broken, let's fix it. To get something new done you have to be stubborn and focused, to the point that others might find unreasonable."

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In the summer of 1994, Mr. Bezos quit his job in New York as a vice president at the financial-services firm D.E. Shaw. He and his wife, MacKenzie, moved to Seattle to take advantage of the explosive growth of the Internet and to start Amazon. The company's original name, Cadabra, was nixed after someone misheard it as "cadaver."