This category is for people who have held the position of President Pro Tempore of the United States Senate.
The office of President Pro Tempore is defined by the United States Constitution as a Senator who serves as President of the Senate in the absence of the Vice President of the United States. In the past, the Vice President routinely filled the duty of presiding over Senate sessions, so it was a fairly meaningless post except on occasions when the Vice Presidency was vacant. Since the 1960s, it has become common practice for the Vice President to preside only on certain significant occasions, such as the first day of a new Senate session, the State of the Union address, or another Presidential address to a joint session of Congress, or when his presence is required or expected to be required to break a tie vote.
However, the President Pro Tempore still does not regularly serve as presiding officer during Senate sessions. That duty is usually rotated among junior senators to help them familiarize themselves with parliamentary procedure.
The President Pro Tempore was once second in line of Presidential succession, following only the Vice President, and was first in line when the Vice Presidency was vacant. In 1886 the President Pro Tempore and the Speaker of the House, who had been next in line after the President Pro Tempore, were removed from the line of succession. In 1947 they were reinstated, but now the Speaker came ahead of the President Pro Tempore.
The President Pro Tempore used to be elected by the Senate, much like the Speaker is elected by the House of Representatives. Today, the title passes automatically to the senior member of the majority party.
In 1977, the Senate created the honorary title of Deputy President Pro Tempore for any former President or Vice President of the United States who served in the Senate after leaving his executive office, regardless of party. As of 2010, the only person ever to have held this office is Hubert Humphrey (D-Minnesota), for whom it was created. Humphrey is one of two people to have held a Senate seat after vacating the Presidency or Vice Presidency. The other is Andrew Johnson (D-Tennessee), who did so before the position of Deputy President Pro Tempore was created.
In 2001, the title of President Pro Tempore Emeritus was created to be given to any member of the minority party who had previously served as President Pro Tempore. The title was purely honorary and connoted no official functions or benefits. The first President Pro Tempore Emeritus was Strom Thurmond (R-South Carolina). From 2001 to 2009, there were three Presidents Pro Tempore Emeritus: Thurmond, Robert Byrd (D-West Virginia) and Theodore Stevens (R-Alaska). When the 111th Congress convened on January 3, 2009, the position was vacant.