In most modern republics, the President is the head of state. Not all modern republics have a President as head of state; examples include the systems used in Switzerland and San Marino. While the Swiss system has a President of the Confederation, the head of state is actually the seven-member Swiss Federal Council. The President is a member of the Federal Council elected by the Swiss Federal Assembly (the Swiss Parliament) for a year; and the President is merely primus inter pares (first among equals).
In states with what is called a Presidental system of government, the President is also the head of government, as well as the head of state. Countries with such a system include the United States. In this system the office of President is very powerful, both in practice and theory.
Other states have what is called a Parliamentary system of government, in which the President is only head of state, and the Prime Minister is the head of government. Countries with such systems include India and Ireland. Under such a system, whatever reserve powers the President may have in theory, the role is in practice largely ceremonial and carries no real power under normal circumstances.
A third system is the French system, in which like the Parliamentary system there is both a President and a Prime Minister, but unlike the Parliamentary system the President has significant real power. This system, which can be considered a hybrid between the first two, was developed at the beginning of the Fifth Republic. It is used (of course) in France, and also in several other countries which have emulated the French model.
In democracies, this is an elected position, elected either directly by the populace, or indirectly by either the legislature or some other body. But the title is frequently taken by self-appointed dictatorial and/or military-backed leaders, as was the case with Fidel Castro in Cuba, or Idi Amin in Uganda.
Presidents of France
Presidents of Germany
Presidents of India
Presidents of Russia
Presidents of the Union of Soviet Socialist Republics
Presidents of the United States of America
Presidents of the European Commission
The President is the chief executive of a corporation, society, public institution or other organised body of individuals. In western corporations, the term is often synonymous with the title Chief Executive Officer (CEO).
CEOs of major corporations