In a mature Knowledge Management framework, we see three chains of accountability (see picture) leading to three sets of roles within the KM organisation.
Ownership, organisation and maintenance of the company knowledge base is the accountability of the functional organisation (orange). Individuals within the functions have accountability for developing and deploying best practice, in order to sustain the capability of the organisation. The chief engineer, for example, is ultimately accountable for the engineering competence of the organisation, and therefore for the state of the company engineering knowledge base. He or she will delegate components of this to individual subject matter experts. In addition, he or she will delegate accountability for coordinating the communities of practice which cover engineering topics. These roles are described further under Communities of Practice, Knowledge Librarians, and Knowledge Owners
The line organisation (green) is accountable for the application of the knowledge in the work of the business, and for the creation of new knowledge. If the organisation has clear KM expectations for project or business activity (e.g. that every project should have a knowledge management plan, or that each project stage should be closed by a Retrospect) then the accountability for the line organisation is to meet these expectations. The accountability will probably lie with the project managers, though he or she may delegate some of the KM activity to a delegate (a project knowledge manager for example). These roles are discussed further under Knowledge Managers.
The nature of the central organisation will change as Knowledge Management is implemented. Initially you will need a KM implementation team to set up the Knowledge Management strategy and framework, and to run the KM implementation project. Once the framework is implemented, the implementation team hands over to a KM support team (yellow). This team is responsible for ensuring that the KM system itself (the tools, the processes, the technologies) are fit for purpose, and are well understood and applied, and for operating the KM Governance system.