In The Mercenary Prince, Delvin Cunningham goes on his adventure to prove to himself that he has what it takes to be a champion. Luke Callindor starts his adventure to prove he deserves his famous surname. Nyx has been raised to save the world while Fizzle is more interested in protecting his friends. Sari has become a hero out of fear of being left behind by her remaining loved ones, Timoran Wrath is honor bound to stand by the others, and Dariana knows no other path. All of these characters hold the role of protagonist in Legends of Windemere, but the all have different reasons. Many times these reasons change as a story progresses.
Looking over the reasoning, I think there’s always a level of selfishness within a hero’s inspiration. He or she either do it for themselves or do it because they feel like they can’t trust anyone else to do it. This might not be as bad as it sounds since things are never as black and white as we’d like to think. Yes, it’d be easier if a hero was truly good and that was the end of it. That tends to be boring too. As much as people want the boy scout in real life, it seems we don’t really like them in fiction. We also tend to distrust them in real life because ‘nobody can be THAT good’. Supposedly.
So an author has to really think about what to do as far as why the character is a hero . . . or not. To be honest, some characters simply fall into their role as you write. For example, Luke and Nyx were planned. Timoran and Delvin kind of just happened as I outlined along. The point still stands that there are different reasons for different heroes, which one should consider in the case of an ensemble cast. It has to be natural too and not forced because that can simply ruin a character.
So, what drives your heroes?