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.
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.