At boarding school, Cavill was prone to homesickness. "I bawled on the phone to my mom four times a day," he says. "I became an easy target." Being Fat Cavill didn't exactly boost the boy's self-esteem, but it did help him form an early understanding of his breakout character's inner life. "My version of Superman," he says, "is essentially of a guy who has spent his whole life alone." Cavill overcame his own loneliness by acting in school plays, several per year, to the point where he decided to focus his studies on drama. At first, his stockbroker father, Colin, discouraged the decision. "He wanted me to get a proper degree first," Cavill says. But then casting agents showed up on campus, looking for teenagers with the right dramatic pedigree and posh enough elocution to join a filmed adaptation of The Count of Monte Cristo. Cavill, then 17, got a part. "My dad," he says, "was like, 'Okay, you have a professional job now, so great, go for it.'" Cavill's path was settled, and the role whipped him into shape. "I lost one and a half stone"—21 pounds—"and I wasn't Fat Cavill anymore," he says, arching an eyebrow and, also, settling on an order. "I'm going for the fish and chips."

The other touchstone moment at boarding school involved Russell Crowe, who plays Cavill's father, Jor-El, in Man of Steel. "He was on campus filming Proof of Life," Cavill says. "Everyone was standing in a semicircle, and I thought, 'We look ridiculous, staring like he's some kind of prize pony.' So I walked up and said, 'Hi, my name is Henry. I'm thinking of becoming an actor. What's the acting world like?' He said something like, 'Sometimes it's great. Sometimes it's not so great. It's fun acting. And they pay well.' Then everyone ran up and asked for autographs, and I turned to Russell and said, 'Run.'" Several days later, Cavill received a package from Crowe containing snacks, a rugby jersey, and a CD of the actor's band. "There was also a signed note," Cavill says, picking up a fry. "It said, 'Dear Henry, a journey of a thousand miles begins with a single step.'" On the set of Man of Steel, Cavill reminded Crowe of their meeting. "I told him, 'I was the fat one who didn't ask for your autograph.' He looked at me blankly, and then he actually remembered."

Crowe's proverbial wisdom proved nearly, if not exactly, prophetic, as Cavill's Superman journey began, in earnest, on his steps. "When I found out I got the part," he says, "I was home playing World of Warcraft. Zack called, and I thought he was calling to let me down easy. But then it dawned on me that he was giving me the part. I had to play it cool. Be appreciative, respectful, professional. But the second we hung up, I just sprinted up and down my stairs cheering and whooping like a madman. I kept looking in the mirror, going, 'I don't believe it. I'm Superman? I'm Superman!'" In fact, he was Snyder's chosen one from the outset—the only actor screen-tested on film by the director for the part.

Cavill credits his early and unlikely confidence to his parents. "They taught me to believe in myself," he says. "And as much as there were times where I really didn't, you muscle through. You end up believing in yourself even more." It's also worth noting that Colin and Marianne Cavill, parents to five boys, are actually in the business of raising sons who look and act like heroes. Cavill's oldest brother, Piers, spent a decade as an officer in the British Army. Nik, the second-oldest, is a highly decorated Royal Marine, having served in Sierra Leone and Iraq and as an infantry commander in Afghanistan.

While nowhere near actually influencing matters of global security, Cavill's work ethic for Man of Steel seems to follow his family's code of honor. "Henry's commitment was legendary," Amy Adams says. "He would get up to work out at three every morning so he'd look right in the suit all day. His discipline is extraordinary." Snyder had a goal in mind for sculpting Cavill's body. "When I was doing 300," the director says, "I wanted the guys looking like they could survive life in the woods, like they could hunt things down and kill them. For Superman, for Henry, you want that . . . and a little more." Since the movie wrapped, Cavill has lost nearly all the bulk he put on. He no longer looks like a man-bear. "I'm not eating 5,000 calories a day anymore," he says. He's also cut back on the grueling Tabata workout methods employed by his trainer, Mark Twight, the record-breaking speed alpinist who has become Hollywood's go-to sensei for creating musculature that looks computer-generated but isn't. Aside from his caloric intake, Cavill, showing both respect for trade secrets and a reasonable fear of Internet trolls, refuses to divulge any additional numbers. "I will say I was a lot bigger as Superman," he says. "A lot bigger. I'm not saying how much. It's modesty about the weight—I've always been worried about my weight—but I also don't want to invite that debate: Henry weighs this, so he's the perfect Superman. Or, Henry doesn't weigh this, and therefore he's not believable in the role."