Carl Trumbull Hayden was an American politician. Representing Arizona in the United States Senate from 1927 to 1969, he was the first U.S. Senator to serve seven terms. Serving as the state's first Representative for eight terms before entering the Senate, Hayden set the record as the longest-serving member of the United States Congress more than a decade before his retirement from politics. He was Dean of the United States Senate and served as its president pro tempore and chairman of both its Rules and Administration and Appropriations committees. He was a member of the Democratic Party. Hayden was also the last remaining member of Congress to have served during the presidencies of William Howard Taft and Woodrow Wilson, as he retired in 1969.

The dean of the United States Senate is an informal term for the senator with the longest continuous service, regardless of party affiliation. This is not an official position within the Senate, although customarily the longest-serving member of the majority party serves as president pro tempore.