There's no way to tell without more information. But it might include the master, and if it's a story about a business master, it could have business partners or rivals as main characters. They would play important roles in the story, either helping or hindering the master's progress in the business world.
As I don't know the details of this 'the master true story', I can't say for sure who the main characters are. It could be the master themselves, of course, and perhaps their mentor if they had one on their journey to becoming a master.
Given the lack of knowledge about this specific story, it could be that the main characters are the master and their family. In many true stories, the family can be a big influence. For example, if the master is a musician, their family might have supported their early interest in music, or maybe there were family members who were also musicians and inspired them.