Stories frequently show how characters grow to become heroes, or demonstrate and prove that a character is a hero. A hero represents an ideal, the ability to set aside selfish desires and work for the sake of others, sometimes sacrificing personal goals in the process. In a word, altruism. Heroes live by a moral code, with the will to endure, resist temptation, and help others.
Admirable Virtues 102-6
Audiences need to like the protagonist(s), to both relate to and admire them. People often relate to characters that remind them of themselves; characters who face similar types of problems. People often admire characters that demonstrate a skill or proficiency, particularly if that skill demonstrates altruistic motives, such as teaching or medicine, or if it has a strong visual appeal, such as performance arts or athletics. Intelligence is another admirable trait, though when it comes to brains a person can be smart, knowledgeable, or clever.