Thomas Jefferson kept a list of them on his wall. So did Albert Einstein. Ralph Waldo Emerson fretted over whether Napoleon was a true one.
Heroes. With all the adulation that's been heaped on second-time astronaut John Glenn - not to mention all the hand wringing over whether there are any truly great men and women around these days - historians say it's worth noting that Americans have obsessed about heroes for centuries.
"There is this kind of hero panic that we're in at the moment," says Sean Wilentz, a professor and director of the American studies program at Princeton University in New Jersey. "But that's a perennial in American history. Each generation seems to go through it."
Jefferson's list of heroes included Francis Bacon and Isaac Newton. Einstein's included physicist James Clerk Maxwell and Mozart. And Emerson, after much wrestling, pronounced in a famous essay that Napoleon was most definitely not a hero (contrary to popular opinion) because he lacked character.
That much said, however, many historians and social observers argue that these are changing times for the American hero - thanks to huge shifts in society, ranging from the explosive immediacy of the Information Age to a post-1960s culture that glorifies the rights of the individual over commitment to a greater common good.
"We're starved for heroes," says Peter Gibbon a research associate at Harvard University who is writing a book with the working title, "Heroism: The Lost Vision of Greatness." Although American-style democracy has always tended to buck the notion that some people are greater than others, Gibbon argues that the nation "is unusually debunking and unadmiring at the end of the 20th century, more so than at any other time in our history."
Gibbon and other critics say that in a media age marked by intense scrutiny of private lives - and a certain rush-to-judgment attitude on the part of journalists and the public - it's almost impossible for individuals to grow to greatness over a lifetime. Nelson Mandela and Mother Teresa are the two contemporary figures most often mentioned by experts as true heroes. But in general, they say, the media have increasingly leaned toward "gotcha" journalism, pouncing on flaws and making little allowance for the complexity of human nature.
"All our heroes will be human," says Mr. Gibbon. "The challenge of our time is to embrace complexity, and still be able to look up and admire.... We should be interested in what makes greatness. Heroes bring out our brave and better selves."
Experts cite the rise of America's celebrity culture as another factor contributing to the hard times for heroism. All too frequently, they say, fame and notoriety are the hallmarks of today's "greatness" - and not the qualities traditionally associated with heroism, such as courage, character, selflessness, and the overcoming of adversity.
"We don't talk about what a virtuous good life is very much," says Kevin Ryan, director of the Center for the Advancement of Ethics and Character at Boston University. "The more materially comfortable we get, the more people are embarrassed about that question.
"In times of warfare, in times of great uncertainty, I think that people who are stepping out and putting their life on the line, or devoting themselves to causes somehow strike the moral imagination more," he says. "But when the good times roll, the virtuous lives are somehow lost."
Marshall Fishwick, a professor of humanities at Virginia Tech who has followed heroes since writing a doctoral dissertation on the subject in the 1950s, says that Americans today "are creating many celebrities, but few heroes."
"We're at a low ebb when it comes to heroes," says Mr. Fishwick. "The 20th century is full of falling stars, of people who rise quickly and shine for a while, but then fall from the scene. It's a very serious matter," he says. "Because we need heroes. We need to look up to something greater, something larger than we are."
Yet historians do note some positive trends. They say America's growing diversity means that white, male leaders aren't the only candidates for hero status now. Women and minorities are increasingly held up as heroic, as recent biographies have shown, including those on Sojourner Truth and Helen Keller.
This "democratization" of the hero also lends itself to greater appreciation of heroic acts at a local level - and to strong bonds between children and parents or teachers. "We've developed a more balanced vision of what a hero is," says Mitchell Stephens, whose recent book, "the rise of the image the fall of the word," examines hero-building and the media.
"I think humankind has grown up a bit," he says. "We're learning that these people are not more saintly than we are. We can have a democracy of [heroes], as well as political democracies. It's healthy."
During times of peace, historians say, different kinds of heroes emerge.
While not exhibiting the kind of bravery and selfless commitment to a higher cause associated with traditional heroes, they say, people such as basketball star Michael Jordan exemplify a sports hero. Microsoft founder Bill Gates is often mentioned as a possible inventor-hero.
Despite all the changes in recent decades, though, many observers say heroes will rise again - when the country faces a severe challenge of one kind or another. "There's plenty of room for heroes," says Princeton's Wilentz. "The times will call them up."