Henry Worsley himself had made two previous journeys on the continent. The first, in 2008 and 2009, was in commemoration of Shackleton’s journey a century earlier. Mr. Worsley retraced the original route through the Transantarctic Mountains and across the Beardmore Glacier. The party arrived at Shackleton’s farthest point south — 97 miles from the South Pole, where he “shot his bolt” — exactly 100 years to the day after Shackleton did, and then proceeded to finish what Shackleton did not.

Mr. Worsley’s second trip, leading a team of six in 2011, celebrated the centennial of the journeys led by Robert Falcon Scott and Roald Amundsen, who reached the pole within five weeks of each other. Mr. Worsley, traveling with others, followed the Amundsen route from the Bay of Whales across the Ross Ice Shelf.

An undertaking requiring enormous physical strength and stamina, Mr. Worsley’s final journey was “a feat of endurance never before achieved,” as he described it. (A Norwegian explorer, Borge Ousland, crossed Antarctica alone and unsupported in 1996-97, but he used a kite to pull his sled. In 2012, a British woman, Felicity Aston, skied alone across Antarctica, but she had two supply drops.)

Mr. Worsley began his trek in November on Berkner Island, which is surrounded by an ice shelf. Braving temperatures of 40 degrees below zero and attenuated air at elevations above 9,000 feet, and buffeted by sometimes brutal winds, Mr. Worsley wore mountaineering skis and hauled a supply sledge with gear — including a tent, electronic communications equipment, climbing apparatuses for ascents and enough food for 80 days — that weighed over 300 pounds. He walked on a normal day for 13 hours.

On Jan. 2, Day 51, he reached the pole and was greeted by staff members of the Amundsen-Scott South Pole Station, the first people he had seen since his departure. He had to resist taking any food or supplies from them, he said, to maintain the integrity of his unsupported and unassisted journey.