The Scrum Alliance Official graphic The Three Roles Of Scrum
The Scrum Master - "The Transmitter"
The advocate and servant leader for the team
Keeps communications flowing between the Product Owner and the Development Team
Protects the process by keeping Scrum Events and Artefacts on track and on schedule
The product owner - "The Translator"
Keeps communications flowing between the Stakeholders and the Scrum Team
Decides WHAT the highest priority items are for the team to work on.
Makes sure the whole team is always working on delivering VALUE.
Development Team - "The Specialists"
Naturally self-organising and determines HOW the highest priority work will be completed.
Is cross-functional... meaning has all the skills needed to complete the agreed work.
Accepts guidance in Scrum in a flat hierarchy with the Scrum Master and Product Owner.