An Assistant to the President, or AP is the highest level of organizational leadership within a mission next to the Mission President, as the name suggests. This is an assignment from the mission president and not a calling. This assignment is typically given to young male missionaries who have shown themselves capable of the requirements of a responsible leadership role, have demonstrated reasonable obedience, and whose talents and abilities are not needed more in a different role within the mission.
In many missions an AP is chosen from among the missionaries who have been in the mission the longest. Although an AP may remain in the position until the end of his mission, some missions allow a missionary to serve in other capacities after having served as an Assistant. APs supervise many of the affairs of the missionaries in a mission. Most missions have 2 APs, but the number and how they function may vary. They are accountable to the Mission President in their mission and generally supervise the activity of the Zone Leaders.