I watched a program on Discovery a few months ago about life in the middle ages.
At that time many peasants were owned by the lord of the manor, and a peasant needed his permision to marry, move house and so on.
Often the peasant was given a house and some land, with the agreement he would do work for the land owner (perhaps work on his land for so many days of the week).
Sometimes a peasant would have an argument with his lord of the manor, and so in the middle of the night the peasant would do a runner.
The peasant could not go and live on land owned by another lord or he would be sent back to his original lord, so often they would hide out in the forrests (England was covered in forrests in the middle ages).
In those days the forrests were owned by the King and his lords, and were used for hunting (Deer or Boar and so on), and it was illegal for a commoner to go into the forrests and kill deer and other animals (punishable by death).
The King had men who would patrol the forrests and look out for poachers, and anyone found hunting deer could be killed, or have their hands choped off.
So the commoners who had chosen to live in the forrest set themselves up into gangs, and they would kill the Kings deer and other animals.
Of course the Kings men would try to catch them in the act, so a sort of cat and mouse situation arose.
These gangs in the forrest soon became the stuff of legend, and many stories and poems were written about them, or passed on by word of mouth (most people could not read at that time).
So Robin Hood was one fictional character who became a "hero", killing the Kings deer and givng it to the poor, plus having exciting adventures trying to evade the kings policemen.
It is the stuff of legend.