Robert Byrd.
Each state has 2 senators. The one who has been in office the longest is the senior senator.
Yes she is the senior Senator and Susan Collins is the junior Senator.
When Jim Webb did not run for reelection in 2012, Mark Warner, who is still in his first term (2009-2015), became the senior senator from Virginia.
Bill Nelson (D) is the senior US Senator from Florida.
Each state has two senators a Junior Senator and a Senior Senator and there is 50 states so there is 100 Senators throughout the entire United States.
Sen. Richard J. Durbin (D-IL). He is also the current Majority Whip.
The difference is that the senior Senator has been in office longer than the junior Senator.
Maryland senior senator is Sen. Barbara Mikulski. Maryland junior senator is Sen. Bejamin Cardin.
The current (2010) Senate Majority Leader is Harry Reid and the President Pro Tempore who by custom is the Senior Senator is Robert Byrd.
State Senator
Alabama's senior senator is Richard Shelby
My two Legislative representatives for Florida are senior Senator Bill Nelson and junior Senator George LeMieux.