I'm not much of a rock climber... and certainly not a big-wall climber. This is not modesty. Sixteen expeditions to 8,000-meter peaks—nine of those to the top of Mount Everest—and 22 years spent guiding cold, remote glaciers don't make one modest. But it can make for a less-than-all-around climber, which is me, because big-wall climbing and high-altitude mountaineering require surprisingly different skill sets. Sure, when I started going up mountains I dreamed of climbing Yosemite's El Capitan. But let's face it: I also wanted to be a fighter pilot, the president, and a porn star. I became an Everest guide instead.

Eleven years ago, in Antarctica, Alex Lowe, the quintessential all-around climber, watched me tiptoe across steep, blue ice on crampons and noted that I seemed overly concerned with the 5,000-foot drop below me. Right then, he and Conrad Anker, his best friend and longtime climbing partner, offered to take me up El Cap. "Climb El Cap and you'll get comfortable with exposure once and for all," Alex said.

I shouldn't have waited. Alex died tragically in an avalanche two years later, in 1999. Conrad and I had climbed together again earlier that year, when he found George Mallory's remains at 27,000 feet on Everest. We summited together on that trip, and I had a rough time at 29,000 feet. I was badly anemic, I ran out of oxygen, it started to snow, and it was late in the day. Conrad stuck with me. He gave me his own oxygen, and we made it down. He probably saved my life.

Although the El Cap subject came up over the next few years, I didn't figure it was ever going to happen. Then I guided a trip on Everest last year with photographer and climber Jimmy Chin, and while we were wedged in a tent at 20,000 feet, I got to talking about my life's dreams. Jimmy stopped me when I got to the El Cap part. "Rad will guide you, and I'll shoot pictures," he said.