Sometimes no matter how successful we are, we need someone who can help us improve.
Of course the best mentor is our following, because they give us the right feedback about our content. But still, when there is someone more experienced than us, it's better to learn from him/her.
I can't say that I have a mentor, and of course being our own mentor is the best thing we can do. But when there is a content creator who's doing what we expected, and what we liked to be done, we try to do the same or even being better.
For me my mentors are those who inspire me. Those who I can't stop consuming their content. Those who I'll never unfollow unless I see them changing a lot. When I see them following all the principles they always created for, that what makes me so happy about them.
Especially I like to follow the independent thinkers, who base their content on their own research, but not having the same source of the information again and again. I like those who are not influenced by someone, or something, but sharing their own truth.
There is also a kind of hierarchy of mentors : Ourselves and own experience, our followers and their feedback, those who we follow and their content.