ITIL Positions & their weight

There are a lot of ITIL positions in the ITIL-world, each one with a clear definition of the roles & responsibilities.

Apart from the service manager position, that is who leads the work done in the framework (I know, I know,… ITIL does not like to be called “framework”… best practices!!!) for the rest of the positions,

what are the more relevant positions???

Is there a clear hierarchy? or it depends of the implementation of the account and the weight of each role?