The chairman of a company or organisation is the head of a board or committee who has been elected by members of that board or committee. The essential duty of the chairman is to keep the board organised, informed and on task, though frequently there is some degree of public relations work involved as well, in addition to acting as an adviser to the CEO. While it's an oversimplification to suggest that the role of a chairman is simply to be a link between a company CEO and the company board/general public, being an intermediary between these two camps is certainly a central duty of a chairmanship.
Facilitate/Preside Over Meetings
Chairmen are required to "chair," or facilitate and preside over, company board meetings. More specifically, a chairman is expected to determine the agenda of the meeting at hand, encourage discussion and participation from all directors and board members and relay pertinent information regarding current events within or pertaining to the company.
A chairman is also expected to point issue discussions and debates toward a consensus stance, upon which the majority of the board agree, and which can therefore be acted upon for the expected benefit of the company or organisation.
Organising The Board
For productive meetings to take place, the board in question needs to consist of an effective balance of members in regards to the board members' ages, work experience and personalities. This organizational or compositional process is ongoing; as a person carries on in their role of chairman, they will find that board members will either leave of their own volition or will need to be replaced. Additionally, a chairman needs to involve directors already on the board to mentor new directors who are new to their position.
Depending on the company or organisation, the scope and frequency of public relations duties for a chairman may range from practically nonexistent to major responsibility. The spokesperson responsibilities of a chairman generally involve relaying the mission statement of the company or organisation to the public, along with adequately describing to the public the policies of the company or organisation. In times of controversy, the role of the chairman in relaying timely information to the public is highly important, as well as possibly delicate for the chairman in question, given that in times of crisis, they may be seen as the "face" of the troubled company.