The functions exercised by a president vary according to the form of government. In parliamentary and semi-presidential republics, they are limited to those of the head of state, and are thus largely ceremonial. In presidential republics, the role of the president is more prominent, encompassing also (in most cases) the functions of the head of government. In authoritarian regimes, a dictator or leader of a one-party state may also be called a president, often charismatically.
The title president is derived from the Latin prae- "before" + sedere "to sit." As such, it originally designated the officer who presides over or "sits before" a gathering and ensures that debate is conducted according to the rules of order (see also chairman and speaker), but today it most commonly refers to an executive official in any social organization. Early examples are from the universities of Oxford and Cambridge (from 1464) and the founding President of the Royal Society William Brouncker in 1660. This usage survives today in the title of such offices as "President of the Board of Trade" and "Lord President of the Council" in the United Kingdom, as well as "President of the Senate" in the United States (one of the roles constitutionally assigned to the vice president). The officiating priest at certain Anglican religious services, too, is sometimes called the "president" in this sense. However, the most common modern usage is as the title of a head of state in a republic.
In pre-revolutionary France, the president of a Parlement evolved into a powerful magistrate, a member of the so-called noblesse de robe ("nobility of the gown"), with considerable judicial as well as administrative authority. The name referred to his primary role of presiding over trials and other hearings. In the 17th and 18th centuries, seats in the Parlements, including presidencies, became effectively hereditary, since the holder of the office could ensure that it would pass to an heir by paying the crown a special tax known as the paulette. The post of "first president" (premier prsident), however, could only be held by the King's nominees. The Parlements were abolished by the French Revolution. In modern France the chief judge of a court is known as its president (prsident de la cour).
The first usage of the word president to denote the highest official in a government was during the Commonwealth of England. After the abolition of the monarchy the English Council of State, whose members were elected by the House of Commons, became the executive government of the Commonwealth. The Council of State was the successor of the Privy Council, which had previously been headed by the Lord President; its successor the Council of State was also headed by a Lord President, the first of which was John Bradshaw. However, the Lord President alone was not head of state, because that office was vested in the council as a whole.
The modern usage of the term president to designate a single person who is the head of state of a republic can be traced directly to the United States Constitution of 1787, which created the office of President of the United States. Previous American governments had included "presidents" (such as the president of the Continental Congress or the president of the Massachusetts Provincial Congress), but these were presiding officers in the older sense, with no executive authority. It has been suggested that the executive use of the term was borrowed from early American colleges and universities, which were usually headed by a president. British universities were headed by an official called the "Chancellor" (typically a ceremonial position) while the chief administrator held the title of "Vice-Chancellor". But America's first institutions of higher learning (such as Harvard University and Yale University) didn't resemble a full-sized university so much as one of its constituent colleges. A number of colleges at Cambridge University featured an official called the "president". The head, for instance, of Magdalene College, Cambridge was called the master and his second the president. The first president of Harvard, Henry Dunster, had been educated at Magdalene. Some have speculated that he borrowed the term out of a sense of humility, considering himself only a temporary place-holder. The presiding official of Yale College, originally a "rector" (after the usage of continental European universities), became "president" in 1745.
A common style of address for presidents, "Mr/Mrs. President," is borrowed from British Parliamentary tradition, in which the presiding Speaker of the House of Commons is referred to as "Mr/Mrs. Speaker." Coincidentally, this usage resembles the older French custom of referring to the president of a parlement as "Monsieur/Madame le Prsident", a form of address that in modern France applies to both the President of the Republic and to chief judges. Similarly, the Speaker of the Canadian House of Commons is addressed by francophone parliamentarians as "Monsieur/Madame Prsident(e)". In Pierre Choderlos de Laclos's novel Les Liaisons Dangereuses of 1782, the character identified as Madame la Prsidente de Tourvel ("Madam President of Tourvel") is the wife of a magistrate in a parlement. The fictional name Tourvel refers not to the parlement in which the magistrate sits, but rather, in imitation of an aristocratic title, to his private estate.
Once the United States adopted the title of "president" for its republican head of state, many other nations followed suit. Haiti became the first presidential republic in Latin America when Henri Christophe assumed the title in 1807. Almost all of the American nations that became independent from Spain in the early 1810s and 1820s chose a US-style president as their chief executive. The first European president was the president of the Italian Republic of 1802, a client state of revolutionary France, in the person of Napoleon Bonaparte. The first African president was the President of Liberia (1848), while the first Asian president was the President of the Republic of China (1912).
In the twentieth and twenty-first centuries, the powers of presidencies have varied from country to country. The spectrum of power has included presidents-for-life and hereditary presidencies to ceremonial heads of state.
Presidents in the countries with a democratic or representative form of government are usually elected for a specified period of time and in some cases may be re-elected by the same process by which they are appointed, i.e. in many nations, periodic popular elections. The powers vested in such presidents vary considerably. Some presidencies, such as that of Ireland, are largely ceremonial, whereas other systems vest the president with substantive powers such as the appointment and dismissal of prime ministers or cabinets, the power to declare war, and powers of veto on legislation. In many nations the president is also the commander-in-chief of the nation's armed forces, though once again this can range from a ceremonial role to one with considerable authority.