Every organization may have a different structure of the Scrum team but the following three roles are a must,

Development Team
Development ‘Team’ is obviously not one person. This team may also be known as Engineering Team with members from different expertise and job titles coming together. Note that the entire Development Team participates in the Scrum events
Product Owner
Product Owner is a single person and not a team. Product Owner basically helps the team understand the user requirements so that they deliver the most valuable product. Product Owner works with the team every day to ensure Product Backlog is well understood. This role helps the team build the most valuable software they can. Remember the 1st Agile Principle?
Scrum Master
Scrum Master helps the Development Team and Product Owner (and the rest of the organization) to do ‘Scrum’ right. Scrum Master is a leader but his/her leadership style is servant leader. This basically means the Scrum Master spends all his time ‘serving’ the Scrum Team and the organization at large.
Scrum Master Job Description
- Helps Product Owner find effective ways to manage the Product Backlog
- Helps Development Team understand the Scrum events. Facilitate those events
- Helps the organization at large understand Scrum
- Helps the Scrum Team do their best job to deliver the most valuable software possible
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