The office is Senate pro tempore. He is elected by the Senate. The current custom is to elect the majority party member with the greatest seniority in the Senate.
That's the Senate President Pro Tempore.
The "President of the Senate" (who is the elected vice president of the United States, though he or she only votes in the case of a tie, and rarely presides over legislative proceedings), and the "President Pro Tempore," who is a senator who is elected by other senators to lead the senate in absence of the President of the Senate. It is the custom nowadays to always elect the majority party member with the longest seniority in the Senate.
The Vice President of the US is the Senate President, however, he can appoint or delegate any of the senators to officiate on his absence which is called the President's Pro Tempore. The 113th Congress Presidents Pro Tempore as Jan 3, 2013 is Patrick J. Leahy.
James Garfield was a member of the House when he was elected president in 1880.( He was also elected to the senate at the same time, but refused that office to become President. )
The vice-president of the United States serves as the president of the Senate. He is elected by the electoral college that elects the President of the US. He is not a senator and can only vote in the case of a tie. The president pro-tempore is elected by the Senate from among its members. By tradition they elect the majority party member with the longest seniority in the Senate.
The president pro tempore of the Senate is elected by the Senate, and by tradition the majority party elects their party member who has the longest seniority in the Senate. He is a voting member of the Senate unlike the VP. Most of the time who presides over the Senate is irrelevant.
The President pro tempore of the Senate presides over the Senate in the absence of the Vice President. This position is usually held by the most senior member of the majority party in the Senate. The President pro tempore has the authority to lead the Senate and perform duties such as recognizing members to speak, making parliamentary rulings, and directing the legislative process.
The president pro tempore, or president pro tem, will fill in as president of the Senate until the vice president returns. Only elected and active senators can fill this role. The president pro tempore is typically a member of the majority party who has been in continuous service as a senator for longer than any of his or her party peers.
In the US, you become President of the Senate by becoming vice-President of the United States.
The president of the Senate is the Vice President of the United States. When the VP is not there (which he usually is not), the Senate is presided over by the President Pro Tempore. This position is elected by the Senate and is usually the most senior member of the majority party. Currently, the President Pro Tempore is Daniel Inouye of Hawaii.
The U.S. Vice President is the President of the Senate, but does not have any voting power and cannot be a deciding vote in the event of a tie.
The vice-president is elected by the electoral college. He is not appointed by the President and so does not need confirmation by the Senate.
The President pro tempore is the second highest ranking official of the United States Senate . He is a senator who is elected to his position by the Senate.In actual practice it is not unusual for the vice-president and pro temp to both be absent. In that case another senator or, I think, one of the staff serves as time-keeper and keeps track of who has the floor.