President of Earth

By the 26th century Earth was ruled by a president. While head of the Earth Empire, in purely military matters the President was unable to overrule the head of the military with the backing of the Earth Senate.

In 2540 the president came under great pressure to declare war on the Draconians, especially from General Williams, but was able to maintain peace thanks to the Third Doctor. (DW: Frontier in Space)

At some point Duncan Levinson was president of Earth. (Scorpius)