Ex officio member
An ex officio member is a member of a body (a board, committee, council, etc.) who is part of it by virtue of holding another office. The term is Latin, meaning literally "from the office", and the sense intended is "by right of office"; its use dates back to the Roman Republic.
A common misconception is that the participatory rights of ex officio members are limited by their status. This is incorrect, although their rights may be indeed limited by the by-laws of a particular body. Robert's Rules of Order, Newly Revised (10th ed.), clarifies that the term denotes only how one becomes a member of a group, not what one's rights are. It is a method of sitting on a committee, not a class of membership (466-67). Frequently, ex officio members will abstain from voting, but unless by-laws constrain their rights, they are afforded the same rights as other members, including debate, making formal motions, and voting (466-67; 480).
For profit and non-profit use 
The power of a person's right to use the title ex officio, in Boards of Directors (Corporations, both for profit and non-profit), and Boards of Trustees (Charitable Organizations, Membership based, Society, etc.) is usually established in the Articles of Incorporation, or in some other foundation governance document.
In some organizations, the term is limited to those who are past Board Presidents, or retired Board Chairs (or Chairwoman, or Chairman) as a reward for serving in a leadership position. An organization may have one ex officio member (the most current past president), or may consider all past leaders as ex officio; again, this is usually detailed in the Articles of Incorporation.
Governmental Examples 
Mainland China 
Hong Kong 
As of 2007[update], the Executive Council of Hong Kong is still composed of ex officio members (official members since 1997) and unofficial members (non-official members since 1997). By practice the ex officio members include the secretaries of departments, i.e. the Chief Secretary, the Financial Secretary and the Secretary for Justice. Since 2002 all secretaries of bureaux are also appointed by the Chief Executive to be official members of the Executive Council. But since 2005 the secretaries of bureaux attend only when items on the agenda concern their portfolios.
New York City 
The Speaker of the Council, and its Majority and Minority Leaders are all ex officio members of each of its committees.
The Manager of Safety in the City & County of Denver is the Ex Officio Sheriff of the jurisdiction. The manager is appointed by the mayor of Denver and oversees the Department of Safety which includes the Fire, Police and Sheriff Departments. Other Colorado sheriffs are elected by the citizens of the county. The City & County of Broomfield, Colorado also has an Ex Officio Sheriff who is the appointed police chief. As the ex officio sheriff, the official is charged with performing the duties of a sheriff per Colorado Sate Law.
The Italian Senate has former presidents of the Republic, and some appointees by the President, as ex officio members.
United Kingdom 
In the House of Lords 26 senior bishops of the Anglican church are ex officio members, and are entitled to vote just as any other member.