A leader is basically someone who has been a superfan long enough. If you’ve been extremely active in a community, it’s easier to get noticed. This person knows the community inside-out and does everything from engagement to being a part of event management.
They have been recognized by community managers as a core, integral part of the algorithm and therefore can be trusted with responsibilities. They are also heavily involved with the decision-making, setting targets, and the overall roadmap of the community.
A superfan (can also be called a creator) is someone who has reached a point where they can influence activity within the community. This person is now a content creator and is always active in the community - asking questions, brainstorming ideas, replying to posts, and reacting to them.