Ambassadors of the United States

Ambassadors of the United States are persons nominated by the president to serve as the United States' diplomatic representatives to foreign nations, international organizations, and as ambassadors-at-large. Under Article II, Section 2 of the U.S. Constitution, their appointment must be confirmed by the United States Senate; while an ambassador may be appointed during a recess, they can serve only until the end of the next session of Congress, unless subsequently confirmed.

Source: Wikipedia — Ambassadors of the United States (CC BY-SA 4.0)