President of Earth (Return of the Klytode)

The President of Earth was the official leader of the Earth's government in 4041. For a while, he was under the influence of the Klytode and worked to have the Klytode Androids in position ready to destroy the Earth's weather control systems. Fortunately, the Tenth Doctor intervened and the President was released from the Klyton’s influence and took responsibility for its safety. (DWAM: Return of the Klytode)

Behind the scenes
This president would seem to have a strong resemblance to Russell T Davies.