Drupal provides fine-grained access permissions, based on 'roles' - basically, classes of users (anonymous, administrators, etc.). Every drupal module has the ability to define permissions.
In this instance, I would create two user roles: primary and secondary.
I would provide the primary role with the permission to 'administer users' (provided by user.module, and includes the ability to create new users, and to change the roles of users).
I would provide the secondary users with the permission to 'access premium content' (which I assume is provided by some third-party module that you are using).
The Primary users would be in charge of creating secondary users, and assigning them the appropriate permissions.
EDIT: I am going to elaborate on my comment below; The Organic Groups module really does exactly what you asked, except with the goal of providing "[A place] ..where subscribers communicate amongst themselves." I am not sure if this is your goal, but it certainly creates a hierarchy of users.
OG is a highly active (read: supported) module, and could probably be considered a sub-project of Drupal itself since it has so many supporting modules of it's own.
HTH