The Leader

In a parallel universe, the Leader was the President of the Republic of Great Britain and was believed to be the third incarnation of the Time Lord known as the Doctor. (PROSE: Timewyrn: Revelation)

Biography
This universe's version of the Second Doctor selected one of the bodies offered to him by the Time Lords after his trial. Like his counterpart, this version of the Doctor was banished to Earth in the 20th century. His TARDIS materialised in England in the 1930s where he became an ally of Oswald Mosley. The two and the rest of the Party's figures were regulars at the Revolutionar Arms pub, and a photo from the time shows the Doctor drawing a beer for one of his colleagues.

After Mosley was assassinated while giving a speech at the Free Trade Hall in Manchester in 1936 he became the new leader of the revolutionary movement helping to craft Mosley's legacy as a martyr of the British people. The Doctor subsequently claimed Mosley's title of "Leader" for himself. (PROSE: I, Alastair)

In 1943, the revolution finally arrived, the old democratic regime collapsed and numerous executions were carried out on the Leader's orders, ostensibly those who had conspired to assassinate Mosley, including among others the British Royal Family. (PROSE: I, Alastair, TV: Inferno)

By 1968, the Leader had become irritable and paranoid, sacking parts of his Cabinet for perceived slights and threats. His health had severely declined and he was more visibly old, now using a wheelchair; he spent two months at Bognor Regis to recover. The Cabinet had started jockeying for power on assumption the Leader wouldn't be around much longer, but he still retained his intelligence. (PROSE: I, Alastair)

The Leader was killed in 1968 when Gordon Lethbridge-Stewart opportunistically used his wheelchair as a battering ram during an alien attack on Downing Street. Photos of the Leader remained omnipresent. (PROSE: Night of the Intelligence, I, Alastair)

The Seventh Doctor remembered the face on the poster in the hut at the Inferno Project and noticed its similarity to the one offered to him by the Time Lords, concluding the Leader was an alternative incarnation of his. (PROSE: Timewyrm: Revelation, TV: The War Games)

Behind the scenes

 *  Revelation is not specific about which of the faces offered by the Time Lords in The War Games was chosen. It likely is the third one, rejected by the Second Doctor for being "too thin", but the fourth of the five proposal, which was "too young", is not displayed on-screen.
 * Photos of the BBC special effects designer Jack Kine were used to depict the Leader on the UNITY IS STRENGTH poster in the Technical Stores, the Doctor's hut on the regular Earth timeline; and the framed photograph on the wall of Brigade Leader Lethbridge-Stewart's office in Inferno. However, the Leader never appears on-screen in person and there is no on-screen evidence to suggest that the Doctor and the Leader had any connection; this connection was made only in the novels.