Bill Clinton

Bill Clinton was President of the United States in the 1990s, between George H. W. Bush and Tom Dering. (EDA: Interference - Book One) The Eighth Doctor explained the Guardian of the Solar System's role in the Galactic Federation in 3999 to Samantha Jones by comparing it to Clinton's role in the United Nations during Sam's time. The Doctor referred to Clinton as "Billy." (EDA: Placebo Effect)

Behind the scenes
The reference in Placebo Effect to real-world President Clinton being president in 1997 introduces a possible discontinuity, as previous and subsequent novels in the BBC Eighth Doctor Adventures established the fictional Tom Dering as US President during Sam's "present day" of the late 1990s. In other parts of the BBC Eighth Doctor Adventures continuity, the clear implication is that Clinton either lost or did not contest a 1996 re-election bid, which allowed Dering to succeed him. (EDA: Interference - Book One, Option Lock)