The ceremonial post of Deputy President pro tempore of the United States Senate was created for Hubert Humphrey, a former Vice President, in 1977 following his lost bid to become the Senate majority leader. The Senate resolution creating the position stated that any former presidents and vice presidents serving in the United States Senate would be entitled to this position. Since Humphrey's death in 1978, no other former President or Vice President has served in the Senate.

The compensation granted to the position holder equals the rate of annual compensation paid to the Senate President pro tempore, Majority Leader, and Minority Leader [1].

During the 100th Congress (1987-1988), George J. Mitchell was elected Deputy President pro tempore by the Senate, due to the illness of President Pro Tempore John C. Stennis. In a similar situation in June 1963, Senator Lee W. Metcalf was designated as Permanent Acting President pro tempore due to the illness of Senator Carl T. Hayden. Senator Metcalf retained this title and frequently presided over the Senate until his death in 1978.

From June 6 2001 until January 3 2003, Senator Strom Thurmond was given the honorary title of President pro tempore Emeritus.

Reference

Congressional Research Service, The President Pro Tempore of the Senate: History and Authority of the Office