Mr. President (title)
Adopted in the 1790s by George Washington, the first President of the United States, as his official manner of address as head of state, "Mr. President" has subsequently been used by other governments to refer to their heads of state. It is the conventional translation of non-English titles such as Monsieur le Président for the President of the French Republic. It also has a long history of usage as the title of the presiding officers of legislative and judicial bodies. The Speaker of the House of Commons of Canada is addressed as Monsieur le Président in French, and Mr. Speaker in English.
In the United States
The 1787 Constitution of the United States did not specify the manner of address for the chief executive. When George Washington was sworn in as the first President of the United States on April 30, 1789, the administering of the oath of office ended with the proclamation: "Long live George Washington, President of the United States." No title other than the name of the office of the executive was officially used at the inauguration. The question of a presidential title was being debated in Congress at the time, however, having become official legislative business with Richard Henry Lee's motion of April 23, 1789. Lee's motion asked congress to consider "what titles it will be proper to annex to the offices of President and Vice President of the United States - if any other than those given in the Constitution." Vice President John Adams, in his role as President of the United States Senate, organized a Congressional committee. There Adams agitated for the adoption of the style of Highness (as well as the title of Protector of Their [the United States'] Liberties) for the President. Adams and Lee were among the most outspoken proponents of an exalted presidential title.
Others favored the variant of Electoral Highness or the lesser Excellency, the latter of which was vociferously opposed by Adams, who contended that it was far beneath the presidential dignity, as the executives of the states, some of which were also titled "President" (e.g. the President of Pennsylvania), at that time often enjoyed the style of Excellency; Adams said that the President "would be leveled with colonial governors or with functionaries from German princedoms" if he were to use the style of Excellency. Adams and Richard Henry Lee both feared that cabals of powerful senators would unduly influence a weak executive, and saw an exalted title as a way of strengthening the Presidency. On further consideration, Adams deemed even Highness insufficient and instead proposed that the Executive, both the President and the Vice President (i.e., himself), be styled Majesty to prevent the "great danger" of an executive with insufficient dignity. Adams' efforts were met with widespread derision and perplexion; Thomas Jefferson called them "the most superlatively ridiculous thing I ever heard of", while Benjamin Franklin considered it "absolutely mad".
In past years, some guidebooks on manners maintained that in the U.S., the title should be reserved for the incumbent president only, and should not be used for former presidents, holding that it was not proper to use the title as a courtesy title when addressing a former president. Despite that, all living former US Presidents continue to be addressed as "Mr. President", both formally and informally, and contemporary experts on etiquette now maintain that it is entirely appropriate.
In the United States, the title "Mr. President" is used in a number of formal instances as well: for example anyone presiding over the United States Senate is addressed as "Mr. President." Other uses of the title include presidents of state and local legislatures, however only the President of the United States uses the title outside of formal sessions.
In other countries
Thomas Hungerford, who became the first Speaker of the English House of Commons in 1376, used the title, "Mr. Speaker," a precedent followed by subsequent Speakers of the House of Commons. This influenced parliamentary usage in France.
By the 18th century, the president of a French parlement was addressed as "Monsieur le Président." In Pierre Choderlos de Laclos's 1782 novel Les Liaisons Dangereuses ("Dangerous Liaisons"), the wife of a magistrate in a parlement is referred to as Madame la Présidente de Tourvel ("Madam President of Tourvel"). When the Second French Republic was established in 1848, "Monsieur le Président" became the title of the President of the French Republic.
The Speaker of the House of Commons of Canada, established in 1867, is also addressed as "Monsieur le Président" or "Madame la Présidente" when French is being spoken.
Titles for a president's spouse, if female, have ranged from "Marquise," "Lady" to simply "Mrs." or "Ms."
If male the title of the president's spouse may be "Marquis", "Lord", or merely "Mr.".
President George Washington's wife, Martha Washington, was often called "Lady Washington." By the 1850s in the United States, the term "lady" had changed from a title of nobility to a term of address for a respected and well-mannered woman. The use of "First Lady" to refer to the wife of the President of the United States was popularized about the time of the US Civil War. Dolley Madison, the wife of President James Madison, was remembered after her death in 1849 by President Zachary Taylor as "truly our First Lady for a half a century."
First Ladies are usually referred to simply as "Mrs. [last name]" 
In the case of the United States electing a married woman as President, her husband would presumably be addressed as either First Man or First Gentleman, while the President herself would presumably be addressed as Madam President.
In the media
On November 8, 2016, the night of the 2016 presidential election in the United States, images of leaked pre-printed copies of Newsweek magazine showed the magazine celebrating the win of the Democratic candidate Hillary Clinton, with the cover titled "Madam President". It is common for Newsweek to prepare for the eventuality of either candidate winning, though it was unusual that it was both published and distributed; the cover was pulled from newsstands after the announcement that Donald Trump won the election.
- Williams, Stephen P. (2004). How to Be President. Chronicle Books. p. 56. ISBN 978-0-8118-4316-4.
- Safire, William (November 24, 1991). "On Language; Manhandling the Handlers". The New York Times.
- Wood, Lewis (May 13, 1945). "Mr. President Is correct". New York Times.
- Bartoloni-Tuazon, Kathleen (2014). For Fear of an Elective King. Ithaca: Cornell University Press. p. 89.
- Bartoloni-Tuazon, Kathleen (2014). For Fear of an Elective King. Ithaca: Cornell University Press. p. 86.
- Hutson, James H. (March 1968). "John Adams' Title Campaign". The New England Quarterly. 41 (1): 30–39. doi:10.2307/363331.
- Bartoloni-Tuazon, Kathleen (2014). For Fear of an Elective King. Ithaca: Cornell University Press. p. 57.
- Hart, Albert Bushnell (1897). Formation of the Union, 1750-1829. Longmans. p. 143. ISBN 1-4069-2845-3.
- Martin, Judith (2003). Star-spangled Manners. W.W. Norton & Co. p. 67. ISBN 978-0-393-04861-2.
- Wood, Gordon S. (2006). Revolutionary Characters. Penguin Press. p. 54. ISBN 978-1-59420-093-9.
- Caroli, Betty Boyd (2003). First Ladies. Oxford University Press US. p. 4. ISBN 978-0-19-516676-7.
- Judith Martin (21 October 1992). "Addressing a Former President". The Washington Post. Archived from the original on 10 June 2014. Retrieved 5 January 2013.
- Robert Hickey. "Is a Former President Addressed as President (name)?". Honor & Respect - The Official Guide to Names, Titles, and Forms of Address. Protocol School of Washington. Retrieved 5 January 2013.
- Kerrie Keller (2013-01-05). "Addressing a Former President of the United States". The Emily Post Institute. Retrieved 2013-01-05.
When addressing a former President of the United States in a formal setting, the correct form is "Mr. LastName." ("President LastName" or "Mr. President" are terms reserved for the current head of state.)
- Mayo, Edith (1996). The Smithsonian Book of the First Ladies. H. Holt. p. 33. ISBN 978-0-8050-1751-9.
- "President Donald J. Trump and First Lady Melania Trump Welcome Governors to the White House". whitehouse.gov. Executive Office of the President. 26 February 2017. Retrieved 22 March 2017.
Mrs. Trump added that, “the scents of jasmine and roses fill the air as we give thanks for this great Nation and the glory of renewal.”
- If a male president's wife is the first lady, what would a female president's husband be known as? First man? First gentleman, First what?, The Guardian. Retrieved on April 12th, 2016.
- Greenslade, Roy (2016-11-10). "Madam President: how Newsweek reported a Clinton victory". The Guardian. ISSN 0261-3077. Retrieved 2016-11-17.