“I keep thinking we’ll burst in on him somewhere peaceful in the woods, and he’ll give us that grin of his,” Luis said. “The one where you can tell he’s thinking, ‘You’re such a dumbass.’”     

But Luis was still anxious enough to keep his ear to his iPhone and his Tahoe hurtling down the highway all night.

IF YOU'VE EVER SEEN the photos that Luis took of Scott Jurek flying across the desert alongside the great Tarahumara runner, Arnulfo Quimare, you’ll understand one reason why Caballo means so much to him. Back in 2006, Luis joined me, Scott Jurek, and one of the founding fathers of minimalist running, Barefoot Ted McDonald, for Caballo’s ultramarathon with the Tarahumara that I describe in Born to Run. Only Caballo’s sheer force of will made the race possible; he’d logged thousands of miles up and down the canyons that winter, visiting one Tarahumara village at a time, earning their trust, and ensuring some of their greatest runners would show up at the start line. The magnificent mayhem of that experience created a kinship that hasn’t faded, I think because it brought out the best in all of us: Scott was extraordinarily noble, Luis took the greatest photos of his career, Barefoot Ted’s kindness found him a true spiritual brother, surfers-turned-ultrarunners Jenn Shelton and Billy Barnett bounced back heroically from near-fatal disaster, and I found myself in the midst of both the story and challenge of a lifetime.

Since then, we’ve yoyo-ed in and out of each other’s lives, and Caballo was often the string that held us together. Caballo and Guadajuko would shack up at Luis’s house whenever they drifted through California, while Jenn, Billy, Barefoot Ted, and I crewed for Luis at the Badwater ultramarathon. Barefoot Ted and I became lifelong friends last summer during a magical night when I paced him to the finish of the Leadville Trail 100. Earlier, Caballo had spent a week in Leadville with me and Eric Orton, the “naked running coach” who persuaded me I could reverse years of injuries and showed me how. We ran trails all day and told stories over beer and jalapeño pizza at night, seeing a warm and fun-loving side of Caballo that had been eclipsed during the chaos of the Copper Canyon race.

So it wasn’t surprising we remained friends; the real shocker was the way Caballo was transformed almost overnight from a lifelong loner into field marshall of an international army of online amigos. For decades, he’d lived like a wanted man; he’d bust his hump as a vagabond furniture mover for a few months in Boulder, then drop off the planet the second he’d saved enough for a year’s frijoles. He’d disappear into the Guatemalan highlands or Mexican canyons, spending his days rattling around the hills and inside his own head. Until he was nearly 60 years old, Caballo split his time between a one-room hut in Tarahumara territory and a sleeping roll in the back of a pickup in Boulder. The Tarahumara were his ideal companions: they ran a lot, spoke little, and never said no to a brew.

But after Born to Run, Caballo was the man in demand. Suddenly, he was jetting off to speaking engagements in London and Stockholm and signing autographs at standing-room-only events. He became an accidental icon, and I loved the way it didn’t soften his raw edges a bit. Minimalist movement? He couldn’t care less, even though he’d been moving minimally for 40 years and had adopted the Tarahumara taste for toe-freeing sandals long before FiveFingers were associated with anything besides shoplifters. He remained searching and skeptical, sunny and surly, a true cowboy who picked his own name, went his own way, and was his own horse. When The North Face offered in 2007 to finance the Copper Canyon Ultramarathon he was struggling to keep alive with his cash, Caballo turned them down, afraid his funky festival in the middle of nowhere would become a corporate-bannered monstrosity with its heart hollowed out by expo booths. His reply summarized his life and became his public identity: “Run Free.”

Caballo was the first runner I’d ever seen who busted out big miles in skimpy sandals, and he opened my eyes to the idea that distance running is humankind’s first fine art; for most of our existence, it was the one natural weapon we had in a world dominated by creatures who could out-swim, out-sprint, out-climb, and out-fight us. I was certain when I went down to the Copper Canyons that I really had nothing to learn: I figured the Tarahumara were genetic freaks and my own running days were over due to chronic injuries. Then I meet Caballo, my eerie astral twin: we were the same height, the same shoe size, and the same age when we first encountered the Tarahumara, and he’d also struggled with broken-down legs. He took me into the hills, showed me a few things, and sent me home with the idea that maybe, just maybe, the Tarahumara were custodians of a transferable skill that even an overweight mope like me could master.

That’s why he has fans all over the world. But right when the rest of us were catching up to him, Caballo disappeared.