Arthur Winters

Arthur Coleman Winters was President Elect of the United States of America circa Spring 2008. After "Harold Saxon" announced the existence of the Toclafane to the world, Winters served as designated United Nations ambassador to the Toclafane.

After Winters angered Saxon (actually the Master), Saxon ordered Winters killed by one of the Toclafane. His death signaled the start of the Toclafane occupation of Earth. (DW: The Sound of Drums)

The Paradox Machine only rolled back time to a few moments after Winters' death, meaning that it still happened. (DW: Last of the Time Lords)

Behind the Scenes
Dialogue in The Sound of Drums refers to Winters as "President Elect" of the United States, rather than the actual President. This would seem to suggest that The Sound of Drums takes place between November 2008 and January 2009 when, in the real world, a new president would have been elected and sworn in, respectively. However evidence in Torchwood and other Doctor Who stories stories indicates the death of Winters occurs in early May 2008, suggesting that, in the Doctor Who Universe, the American electoral system followed a different path. (Winters does not, of course, correspond to the real-life President Elect of 2008, Barack Obama, nor to George W. Bush.)