In my opinion, the below are the key roles in PM:
- The project manager: The project wouldn't be executed without him.
- The client: The project wouldn't exist without him.
- The project sponsor: The project cannot start without him, and it needs his constant support.
- The project stakeholders: The project can be killed at any time if they decide so.
- The project team: No work will be done on the project without them.
- The supplier: The project won't have the material needed without him (note that this roles is mainly relevant to construction projects)