Gene Espy had always been adventurous. He explored caves, rode his bicycle 740 miles from his home in Georgia to Florida and back, and hiked through the Great Smoky Mountains for a week.

But on May 31, 1951, when he was 24, he began a new journey that was even more arduous and seemingly preposterous: hiking the length of the Appalachian Trail, some 2,000 miles, northward from Georgia to Maine, in a single, continuous trek known as a “thru-hike.”

It had been done once before, in 1948, by Earl Shaffer, a Pennsylvanian. But Mr. Espy didn’t know about Mr. Shaffer until a farmer showed him a newspaper clipping while he was already on his expedition.

“He didn’t do it to be the first,” Mr. Espy’s daughter Jane Gilsinger said in an interview. “He did it to have fun and see God in nature.”

She confirmed his death, on Aug. 22, at his home in Atlanta. He was 98.

It took Mr. Espy 123 days to complete his journey, which started at Mount Oglethorpe in Georgia and took him through 14 states along the world’s longest continuous hiking-only footpath. Back then, the Appalachian Trail was mainly rugged wilderness, with few trail markers. He walked through parts of the trail where few others had ventured.

“I’d carry a map in my hat,” he was quoted as saying in 1993 by The News and Observer of Raleigh, N.C. “Every so often, I would stop and take my hat off, pull out my map, look around and try to figure out where I was.”