Who is the president of the most populous country in the world?

Assuming you meant

• country (sovereign state or former sovereign state whose territory is still internationally recognised as a political or cultural entity) and is geographically located (completely) within and the world (the geographical area corresponding to the entire surface area of planet earth)

Did you mean?

• country (sovereign state or former sovereign state whose territory is still internationally recognised as a political or cultural entity)
• sovereign state (a state which is not under the control of any higher level state regardless of the level of international recognition)
• sovereign state recognised by the United Nations