The Speaker of the House is a Member of Congress who serves as the leader of the United States House of Representatives
The position was created by Article I, Section 2 of the Constitution. However it is vague on the particularities of the position, as it is on many other positions, leaving it up to the House to flesh it out. Our Founding Fathers created the position recognizing the need for a leader to run the House. Although a Speaker is not required to be a member of Congress, no Speaker who is not in Congress has ever been elected.
Traditionally the majority party has chosen the Speaker after the biannual Congressional Elections. If the majority party does not have its members vote for their candidate, a minority party member could become Speaker. However this has never occurred in the history of the Union.