William Brangham:

With a final 32-hour 80-mile push, Colin O'Brady became the first person to cross Antarctica alone without any assistance.

The 33-year-old celebrated with a post on Instagram, writing: "I did it."

This was 54 days after setting off on this brutal 930-mile-long trip. Upon arrival, O'Brady tearfully called his wife and expedition manager, Jenna Besaw.

O'Brady started the treacherous journey on November 3 at the Ronne Ice Shelf on the continent's eastern side. He set off at the same time as 49-year-old Louis Rudd, a British army captain who's also trying to make the historic trip.

The two men raced each other for nearly two months, passing over mountains of ice and snow and across the South Pole. Then, O'Brady made it to the finish, the Leverett Glacier at the Ross Ice Shelf, where Antarctica's land mass ends and the ice sea begins.

Others had made the crossing before, but they had assistance with supplies or kites that helped pull them across the ice. O'Brady had none of that help. Most days, he trekked 12 hours, pulling roughly 400 pounds on his sleds.

He climbed up ice ridges, pushed through blinding snow and 30-mile-an-hour headwinds, and had to endure temperatures as low as minus-80 degrees Fahrenheit.

O'Brady consumed around 7,000 calories a day to ensure he had enough energy for the grueling trek. Still, his legs were emaciated by the end.

He dubbed his attempt The Impossible First, which it certainly would have seemed just a decade ago. That's when an accident that burned nearly 25 percent of O'Brady's body, primarily his legs and feet. Doctors warned him he might never walk normally again.

But, after a lengthy rehab, he went on to become a professional triathlete…