An underdog is : 1. One that is expected to lose a contest or struggle, as in sports or politics. 2. One that is at a disadvantage. However some people are very popular with the crowds and are considered a hero even if they lose, because they have tried very hard.

Hi... An underdog is a person or group in a competition, frequently in electoral politics, sports and creative works, who is popularly expected to lose. The party, team or individual expected to win is called the favorite or top dog. In the rare case where an underdog wins, the outcome is an upset. ...

An underdog is anybody who is not expected to win. If two football teams play, for example and one team has one many games and the second very few, the second team would be considered the underdog. An underdog hero would be someone who was not expected to succeed or win, but did anyway. I don't know how it is in other countries, but in the U.S. it is said that "everone cheers for the underdog."

an "underdog" is someone or something that is at a disadvantage and expected to lose In this case, it sounds like the hero is expected to be defeated