As there's no clear information about this 'the challengers true story', the main characters could be adventurers. They might be the ones who dare to step into the unknown and face various challenges head - on. Maybe they have different personalities, some are brave, some are intelligent, and together they form a team of challengers.
I really can't determine the main characters without more details about 'the challengers true story'. However, they could be reformers. People who saw something wrong in their society or field and decided to be the challengers. They would be the ones leading the change, facing opposition from the established forces, but still striving to make things better.