What are the various roles in Six Sigma implementation?

Attaining Six Sigma is team effort and can not be attained individually. Driving Six Sigma itself in an organization is huge project as it involves lot of mentoring and change of attitude of the current workers. So when an organization wants to drive the Six Sigma way they appoint persons with certain roles as defined below.
Executive Leadership includes CEO and other key top management team members. They are responsible for setting up a vision for Six Sigma implementation. They also empower the other role holders with the freedom and resources to explore new ideas for breakthrough improvements.
Champions are responsible for the Six Sigma implementation across the organization in an integrated manner. The Executive Leadership draw them from the upper management. Champions also act as mentor to Black Belts.
Master Black Belts, identified by champions, act as in-house expert coach for the organization on Six Sigma. They devote 100% of their time to Six Sigma. They assist champions and guide Black Belts and Green Belts. Apart from the usual rigor of statistics, their time is spent on ensuring integrated deployment of Six Sigma across various functions and departments.
Black Belts operate under Master Black Belts to apply Six Sigma methodology to specific projects. They devote 100% of their time to Six Sigma. They primarily focus on Six Sigma project execution, whereas Champions and Master Black Belts focus on identifying projects/functions for Six Sigma.
Green Belts are the employees who take up Six Sigma implementation along with their other job responsibilities. They operate under the guidance of Black Belts and support them in achieving the overall results.
Note: - If you are going for project manager position then you will definitely need to prepare yourself in the area of estimation to a good extent. In the coming sections we will run through estimation related questions which are asked for project manager position. Estimation is a real weakness in software industry today. Different technologies, different company approaches and custom processes followed by software companies it still does not have a standard. So we will try to run through the most embraced estimation technologies by software industry.