Leaders are people that can make others work willingly. Managers are people who can manage the team and organize things. Scrum masters would be like leaders because they are leading the team and product owners would be managers.
I believe that it can be a skill or can be something you are born with. I think this way because I have seen leaders since I was a child and I have seen people become leaders through work and effort so that they can become the best leader that they can be.
Hunter keeps talking about influence because it is critical to have to become a leader. I you can't influence how can you do your job as a leader? If you can't influence people how can you get people to work?
I have earned authority only a few times in my life, but I got it due to respect and trust. Now, I may not be the most respectable person or trustworthy, but when I need to be authoritative I will take charge.
My mother has earned authority over me because she brought me into this world. That is really only the only real reason, but it is a pretty good reason.
Leaders are people who need to be able to make others work. They need to be responsible and able to work, themselves. Leaders can be born and can be trained.