The Speaker of the House.
Speaker of the House of the Representatives
The third person in line is the president pro tempore of the US Senate, who is normally the most senior senator of the majority party in Congress.
Thomas Jefferson was the third president; Aaron Burr the third vice president .
I think it may be the President pro tempore, as he is third in line if the President and the Vice President are killed or incapacitated.
The third person in line is the President Pro Tempore of the U.S. Senate, following the Vice President and Speaker of the House.
The president pro tempore of the US Senate is third in line, behind the vice-president and the Speaker of the House of Representatives. At one time, the "pro temp" was second in line, but an obvious conflict of interest occurred when he voted to remove Andrew Johnson from office, so the order was changed.
the speaker of the house
Third in line, after vice-president and speaker of the house.
the house speaker
Thomas Jefferson , who served from 1801 to 1809, was the third US president.
Secretary of State
Thomas Jefferson