acting president
person who serves as President when an incumbent is unavailable
Interim and Acting President of Israel
temporary government posts provided in Israel's Basic Law
Acting President of Pakistan
post provided in Pakistan's constitution
Acting President of Poland
position
Substitute President of Italy
substitute of the President of Italy who acts as President when the actual President can't or is dead
Acting President of the United States
person acting as POTUS when the president is unavailable
Acting President of Russia
acting head of state post in Russia's constitution