The most enduring American hero of the last century is someone who lived half his life in disguise and the other half as the world's most recognizable man. He is not Jack Kennedy or Joltin' Joe DiMaggio, Batman or Jerry Seinfeld, although all of them were inspired by him. It was on his muscle-bound back that the iconic comic book took flight and that the very idea of the superhero was born. He appeared in more movies than Marlon Brando, who once pretended to be his father. He helped give America the backbone to wage war against Adolph Hitler, the Great Depression, and the Ku Klux Klan. He remains an intimate to kids from Boston to Belgrade and has adult devotees who, like Talmudic scholars, parse his every utterance. And he has done it all with a confidence that let him appear publicly with underpants over full-body tights and assume an alter ego who kept pursuing the prettiest girl in town even though he seldom got her.

The most enduring American hero is an alien from outer space who, once he reached Earth, traded in his foreign-sounding name Kal-El for a singularly American handle: Superman.

We celebrate Superman now because he is turning 75 this year, and because Warner Bros. recently released an animated film about the hero and Random House released the first full-fledged biography on him. More to the point, we honor Superman today because he reminds us not just of inspired deeds past but of what it takes to be a hero in 21st Century America.

So how has Superman managed to survive thrive for seven decades and counting?

It starts with the intrinsic simplicity of his story. Little Orphan Annie and Oliver Twist reminded us how compelling a foundling's tale can be, and Superman, the sole survivor of a doomed planet, is a super-foundling. The love triangle connecting Clark Kent, Lois Lane, and Superman has a side for everyone, whether you are the boy who can't get the girl, the girl pursued by the wrong boy, or the conflicted hero. His secret identity might have been annoying if we hadn't been let in on the joke and we didn't have a hero hidden within each of us. He was not just any hero, but one with the very powers we would have: the strength to lift boulders and planets, the speed to outrun a locomotive or a bullet, and, coolest on anyone's fantasy list, the gift of flight.

Superpowers are just half the equation. More essential is knowing what to do with them, and nobody has a more instinctual sense than Superman of right and wrong. Like John Wayne, he sweeps in to solve our problems. No thank-you needed. Like Jesus Christ, he descended from the heavens to help us discover our humanity. He is neither cynical like Batman nor fraught like Spider-Man. The more jaded the era, the more we have been suckered back to his clunky familiarity. So what if the upshot of his adventures is as predictable as with Sherlock Holmes: the good guy never loses. That is reassuring.

So is his uniform. His tights and cape, in radiant primary colors, make Superman as instantly recognizable as Santa Claus - and as comforting. No need to explain who he was. Everyone knew as soon as they saw him. A costume was elevating, the more so when it didn't come with a mask. Just ask Robin Hood and Elvis Presley.

That does not mean he hasn't changed with the times. Superman has evolved more than the fruit fly. In the 1930s two teenagers from Cleveland's Glenville precinct, Jerry Siegel and Joe Shuster, gave America just the crime fighter we needed to take on the robber barons. In the forties he defended the home front while brave GIs battled overseas. For each era he zeroed in on the threats that scared us most, using powers that grew or diminished depending on the need. So did his spectacles, hair style, even his job title. Each generation got the Superman it needed and deserved. Each change offered a Rorschach test of the pulse of that time and its dreams. Superman, always a beacon of light, was a work in progress.

The comic book and its leading man could only have taken root in America. What could be more U.S.A. than an orphaned outsider who arrives in this land of immigrants, reinvents himself, and reminds us that we can reach for the sky? Yet today this flying Uncle Sam is global in his reach, having written himself into the national folklore from Beirut to Buenos Aires. It is that constancy and purity that has reeled back aging devotees and drawn in new ones. It is what makes the Man of Tomorrow timeless as well as ageless.

Larry Tye, is the author of "Superman: The High-Flying History of America's Most Enduring Hero." He will be speaking at the Brattleboro Literary Festival Saturday afternoon.