Sergeant at Arms of the United States House of Representatives

The Sergeant at Arms of the United States House of Representatives is an officer of the House with law enforcement, protocol, and administrative responsibilities. 

The Sergeant at Arms is elected at the beginning of each Congress by the membership of the House.

They are known for announcing "Mister/Madam Speaker, the President of the United States" during the beginning of the State of the Union Address as the President enters the United States Capitol.

Other websites

 Source: United States House of Representatives Sergeant at Arms Fact Sheet (pdf file), via House.gov
Sergeants at Arms official fact sheet, via history.house.gov

*