What does a Scrum Master do?
The Scrum Master is responsible for the Scrum process, for teaching the Product Owner and for teaching the team how to fulfil their roles within the Scrum process. They are also responsible for the changes within the organisation, to help the organisation optimise its ability to realise the benefits of Scrum, both in terms of productivity, in terms of quality and in terms of early realisation of benefit. So to the extent that an organisation is dysfunctional to building software quickly with quality the Scrum Master is responsible for going out and working with the organisation to make these changes happen. So they are a change agent.