Stephen Knight describes Robin Hood’s boldness in his "Robin Hood: A Mythic Biography as, “physical and ethical courage and success in his encounters with strong, oppressive enemies.” So, not only is he a strong and physically powerful character, he's also good, pure and simple. Also, as a side note, I've always thought that his bold character combined with his fabled skill at archery has made him look a bit like a medieval super hero.
But I digress. The point is that Robin Hood exemplified bold living in everything he did. He and his men didn't just rob people. They captured them, blindfolded them, and led them to their camp where they were fed a kingly feast and "asked" for payment for their hospitality later. How many thieves do you know of who serve their victims - even the ones who didn't deserve it? (I should point out here that these details I’m drawing from the original Robin Hood ballads from which the legend stems). When Robin opposed the sheriff, he was always sure to thoroughly humiliate the man before he escaped. Nothing Hood did was subtle. He was extravagant in his rebellion and no one could be in any doubt of what he stood for.
But, his way of rebellion wasn’t the only thing that made him bold. Take a look at his chosen enemies: Prince John, the Sheriff of Nottingham, Guy of Gisbourne (a skillful assassin in the original tale, though his character has been redone in a variety of ways by now), and nearly all men of the cloth (excluding Friar Tuck, of course). These are powerful, dangerous men who had the resources, power, and cunning to make Robin really suffer without suffering the consequences for it themselves. He became an outlaw, though, because his enemies could not catch him.
The life of an outlaw is romanticized through Robin Hood, but imagine for a moment what it would be like to be considered no better than a wolf. Evil. And anyone can slaughter you at any given moment. Hardly a life of peace or luxury. Despite that, Hood has never been a character to be cast down so quickly. He made his life in Sherwood worthwhile and wonderful, continually pressing forward with never a worry about what the men of power might do to him; only of what they would do to others.
Robin Hood is bold because he didn’t hide. True, he had to stay out of reach of foresters and soldiers, but he outright plundered those who deserved it and protected those who needed him. And everyone knew why he did it. Fearing neither retribution nor punishment, he spoke freely of the simple truths he fought for. In a world of corrupt government and religious leaders, he never faltered in his opposition. He even maintained a loyalty to King Richard - a king that most the people didn’t believe in anymore (although, it should be said that Robin Hood tales were originally set during King Henry’s reign, not Richard’s. But whoever the King, Robin was always loyal).
I think the boldness of Robin Hood is a small part of what makes him so enduring. In this world of shifting values, distrust, and cowardice, people want to believe in someone who will stand up for the pure and simple truths no matter what. We all yearn for a hero like him because most of us don't have the courage to be as bold as him.