GILROY, Calif. — Daniel Cormier, the Ultimate Fighting Championship light-heavyweight champion, is built stocky, like a gallon jug of milk. He’s always been built a little like a gallon jug of milk. A shade under 6 feet tall, with a receding hairline, a round belly, white streaks encroaching on his dark beard and a wide, toothy grin as he steps around unopened wedding gifts in his man cave — it’s hard to imagine that this 38-year-old father of two young children is one of the best in the history of mixed martial arts, and is preparing for the pinnacle of a lifetime in combat.

Dozens of photographs, trophies, plaques and medals cover the walls, cataloging his nearly 20 years in wrestling and his more recent ascension to the peak of mixed martial arts.

Yet one wall in the man cave stands apart from the rest. On it, there’s a poster, and six photos, all from the night of Jan. 3, 2015. That is when he challenged Jon Jones, his most hated rival, for the U.F.C. light-heavyweight title. It was a battle, in his mind, of good and evil. But it was also the culmination of a lifetime of hard work and sacrifice in combat, and of years of unimaginable heartbreak and misfortune, from the loss of his infant daughter to the death of his Olympic dreams.

In three photos, Cormier is punching Jones in the face; in two of them, Cormier is lifting Jones in the air above his head; in one, his right foot is connecting with Jones’s jaw. The photos and the belts across the room tell a story of what happened that night. But they don’t tell the true story: Cormier lost. And afterward, Cormier cried.