He's a now-retired Navy SEAL who moved in with a wealthy entrepreneur's family in Manhattan to teach him how to live an inspired life, but whose identity was kept hidden in a book about the experiment.

Now the SEAL has been revealed.

His name is David Goggins, according to the New York Post, and he recently retired from the military after 21 years on active duty, including multiple tours in Afghanistan and Iraq.

The story of how he wound up living with entrepreneur Jesse Itzler is told in Itzler's book, "Living With A SEAL: 31 Days Training With The Toughest Man on the Planet."

Goggins lost significant weight twice in his life--first when he was trying to join the Navy SEALS in the first place and he was in his 20s, and then again later in life once he gained weight while on active duty.

"Anyone can do it. It's not about what you eat, it's about forcing yourself out of the box -- to stop being so comfortable," he said.

According to the Post:

Goggins move[d] into [Itzler's] home at 15 Central Park West, where he lived with his wife and baby, and train him for a month. That was in December 2010. [He's] now an ultramarathon runner, an ultradistance cyclist and a triathlete.

After more than a dozen friends died in Afghanistan, Goggins began to run long distance to raise college scholarship funds for the children of fallen special operations soldiers, through the Special Operations Warrior Foundation. He has raised millions of dollars.

He is also a motivational speaker and part of Marcus Luttrell's 2015 Patriot Tour with Taya Kyle, the widow of "American Sniper" Chris Kyle and author of "American Wife."