There is only one truly crucial component in defining the folk hero, and that has to do with widespread recognition of the person as being heroic. Many people commit acts of kindness or generosity but that alone does not make them a folk hero. When society is able to recognize an important figure by their name, personality, or deeds, then this person has achieved the status of folk hero.
Folk heroes, as long as they have the one aforementioned crucial characteristic, can vary in a few ways. Folk heroes may be real or based on mythology. In some cases, folk heroes may be historical figures. In essentially all cases, though, the nature of the character is exaggerated for the sake of the story. For example, a folk hero might be described as not needing to sleep. Both physical and personality traits are dramatized. Much of what defines a folk hero is the elusive nature of the character. This elusive nature stems from the exaggerated emphasis placed on the character's physical and character strengths and weaknesses.
There are a few common personality traits of a folk hero. Folk heroes tend to be brave and willing to face opposition. Given the exaggerated nature of the folk hero's character, there is strong emphasis placed on these traits in the accompanying stories. Also, because the folk hero does not usually start out as such, but rather gains his status as a folk hero with his motivation, traits such as bravery and motivation to seek change are given a lot of weight and end up defining the folk hero.
The folk hero commonly takes on a role of leadership and protection. In traditional folk hero stories, the common people of society are facing an instance of injustice or corruption. One person ends up being the force to stand up to the oppression and create the change that the people want. This person ends up being defined as a folk hero, because he or she takes on the leadership role necessary to facilitate societal change. This individual is then seen as a protector in the community, giving the individual the status of folk hero.