This category includes individuals who served as Dean of the United States Senate. All of these people held the position in OTL; Harry Turtledove has never identified a character who served as Dean of the Senate in an alternate timeline.
The Dean of the United States Senate is the senator with the most seniority within a session. Unlike the office of president pro tempore, the position of Dean can be held by a member of either the majority or minority parties. The title is conferred automatically on a senator upon reaching the head of the list of senators by seniority.
The Dean of the Senate is a purely honorary title and connotes no official functions whatsoever, lacking even the minor ceremonial role of the Dean of the House of Representatives, whose job it is to administer the oath of office to the Speaker of the House of Representatives on the first day of a new session of that body.
However, as the chamber's seniormost member, the Dean is best-positioned to take advantage of certain perks of seniority in the Senate. These include preferential treatment in choosing committee assignments, right of first refusal of newly available office space, first choice of a desk in the Senate Chamber (though in practice the choice of desk is heavily constrained by customs relating to standing within a party caucus), and ranking in the purely ceremonial United States Order of Precedence as determined by the US State Department's Office of Protocol. (However, if the Dean is a member of the minority party, he will follow the president pro tempore on this list. He will also follow any senators who are former holders of an office which is ranked higher than Senator, regardless of party.)