Most of us have our own rough defnition of heroism — we think we know a hero when we see one. But pinning down those attributes is a challenge; your hero may not look much like mine. So it's worth asking: Are there certain immutable characteristics that have defined heroism across the ages? The men and women on the following pages are individuals of extraordinary distinction, but how do they stack up against the legends of the past? Although there are some timeless, universal qualities known as heroic, throughout history the idea of the hero has fluctuated and evolved to suit the ethos of the times.

The modern concept of the hero would not have been possible without the Renaissance. Previously, the Middle Ages had not looked favorably upon man's achievements. Living under the shadow of human sin, the Roman Catholic scholars of medieval Europe stressed the afterlife. Greatness came from God, not man, so the true heroes of Christendom were the martyrs, missionaries and priests preparing for salvation. The Renaissance challenged this bleak vision. Part of the challenge came from 14th century Italy's rediscovery of the classical literature of ancient Greece and Rome. The histories of Tacitus, the biographies of Plutarch, but above all the letters and speeches of the orator Cicero opened the classical world anew. What they all emphasized was man's capacity for greatness.

It was the Italian poet Francesco Petrarca, known as Petrarch, who ushered in the new humanism. What excited Petrarch was the classical tradition of education — the aim of which, as Cicero had explained, was to cultivate not a narrow range of technical skills, but the single, noble virtue of manliness. This idea of virtus went on to inspire a Renaissance literature of advice books outlining what was needed to foster a well-rounded man. A manly man was proficient in warfare, scholarship, government, letters and even the art of seduction. In the city-states of 15th century Italy arose a new belief in human potential. The modern hero was born, and the ideal of the Renaissance man remains a heroic value today.

From this Renaissance culture — this new stress on the autonomy and virtue of man — came a series of histories in the late 14th century recounting the inspirational lives of great men. Petrarch's De Viris Illustribus (On Famous Men) ignored saints and martyrs, concentrating instead on the achievements of generals and statesmen. For Petrarch, heroism demanded the purposeful display of virtus: from Romulus, the founder of Rome, to the war leader Scipio, Petrarch celebrated heroes who conquered fortune, beat the odds and rose to the top. More than a few of the heroes in these pages fit that description.