From TARDIS Index File, the free Doctor Who reference.

The President of America was the political leader of the United States of America.

List of Presidents

19th century

• Thomas Jefferson - The Doctor assisted him in drafting the Declaration of Independence, decades before Jefferson became president (DW: The Lazarus Experiment - deleted scene)
• Abraham Lincoln (DW: The Chase)

20th century

1960s

• John F. Kennedy (MA: Who Killed Kennedy, DW: Silver Nemesis, DW: Rose)

1990s

• Carroll (DWM: Rennigan's Record)
• Tom Dering (EDA: Option Lock, PDA: Millennium Shock)

21st century

2000s

• Springsteen (NA: Eternity Weeps)
• Norris (NA: Cat's Cradle: Warhead)
• George W. Bush (WC: Death Comes to Time)
• Arthur Coleman Winters (DW: The Sound of Drums) - referred to as "President Elect"; killed by the Toclafane in May of 2008.
• Felix Mather (EDA: Trading Futures)
• Arnold Schwarzenegger (DW: Bad Wolf)
• An unnamed President affected by Martin Trueman's hypnosis (SJA: Secrets of the Stars)
• Barack Obama (DWM: Ghosts of the Northern Line, DW: The End of Time) - along with everyone else on Earth, was turned into a copy of the Master

2010s

• Barack Obama (see above; the events of The End of Time extend into 2010)

Alternate timelines

18th century

• Benjamin Franklin (BFA: Seasons of Fear, BFA: Neverland)

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President (United States of America)