First contact exposes the head-of-state distinction

If aliens asked to be taken to Earth's leader in 2026, whom should they approach?

There is no single world leader: in the United Kingdom the monarch is head of state and the prime minister heads government, while the US president combines those constitutional roles.

The hypothetical turns on constitutional roles rather than a search for the most powerful politician. For a formal British introduction in 2026, King Charles is the head of state. In the United States, the president combines the roles of head of state and head of government. The Speaker of the House leads a legislative chamber and is therefore not an equivalent national representative. Diplomatic protocol depends on constitutional structure as well as political influence.