President of Earth

The President of Earth was a title held by one person at a time, under special circumstances during the 21st century and on regular basis by at least the 26th century, and again from the 41st century onwards.

Conception
The position of Earth president originated in the early 21st century, before the establishment of a unified Earth government. Organised by UNIT, an international agreement was made on incursion protocols. Under this agreement, in the event of a full-scale invasion, a President of Earth with complete authority over every nation state was immediately inducted. It was decided the only practical candidate for this role was the Doctor. As Earth president, the Doctor would essentially be the Chief Executive Officer of the human race and the Commander-in-Chief of every army on Earth, under whom all world leaders would await instructions.

This induction was performed during an invasion of Earth by an army of Cybermen converted from the dead by a female incarnation of the Master. Having stumbled upon the invasion, the Twelfth Doctor was captured by UNIT and taken aboard their presidential aircraft, Boat One, where he was inducted as Earth president. (TV: Death in Heaven)

Earth government
Both Earth and the broader Earth Empire, and later the Earth Alliance were ruled by this elected figure. However, at least some of the later human empires were instead headed by emperors.(TV: Frontier in Space, Nightmare in Silver)

He or she did not, however, have full control over every aspect of the Empire. In purely military matters, the president was unable to overrule the head of the military without the backing of the Earth Senate. Also, the President of Earth had limited control over the affairs of the planets, like Sirius IV: dominions were semi-autonomous and the president had no control over their domestic affairs. (TV: Frontier in Space)

The president led a democracy, and had to submit to periodic election cycles in which various candidates argued their positions in order to win popular approval. Earth Security was a shadowy police organisation which could hold troublemakers without trial. In extreme cases, the president had the power to remove political rivals to the Lunar Penal Colony for the rest of their lives. The position thus had elements of democracy and dictatorship about it. (PROSE: Doctor Who and the Space War)

History
In the early 21st century, the Twelfth Doctor was temporarily appointed President of Earth during the invasion of Cybermen. (TV: Death in Heaven)

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

Earth's Presidency was based in the White House in Washington DC during the Orion War of the early 26th century, when Duncan Levinson was President of Earth. (AUDIO: Scorpius) Upon Levinson's death, Karen Brett took Presidential office. (AUDIO: Fear)

A clone of Bernice Summerfield became President of Earth in the 27th century. (The Final Amendment)

By the 40th century, the government of Earth was instead headed by a Guardian of the Solar System. (TV: The Daleks' Master Plan) However, 41 years after Mavic Chen's demise in 4000, the title of Earth's head of state was again President of Earth. In the year 4041, the current President was still based in the Oval Office of the White House, where he was secretly under the control of the Klytode until the Tenth Doctor freed him. (COMIC: Return of the Klytode)

Sheridan Moorkurk was elected to the presidency unexpectedly due to a surge in the protest vote against the Conglomerate. (AUDIO: War Against the Laan)

EP One was the President's personal jet. (AUDIO: War Against the Laan)