Mr. Saxon

Mr. Harold Saxon (DW: The Lazarus Experiment) was a politician on Earth. He was active from at least April 2007 when he started campaigning (DW: Love & Monsters) and was elected Prime Minister in 2008 (DW: The Sound of Drums / Last of the Time Lords). He took his campaign seriously, placing posters on walls across Great Britain. (TW: Captain Jack Harkness, DW: Smith and Jones)

He claimed that extraterrestrial life did exist, making him more popular in early 2008 after reports from the Royal Hope Hospital about the Judoon on the Moon (DW: Smith and Jones). Earlier, he also ordered the destruction of the Racnoss Webstar on Christmas Eve 2007. (DW: The Runaway Bride)

Behind the Scenes
"Mr. Saxon" was the arc word for the late part of series 2 and all of series 3 of Doctor Who, just like "Torchwood" and "Bad Wolf" had been for the previous series The phrase also featured in Torchwood series 1, on campaign posters.

It has been theorised that Mr. Saxon is actually the renegade Master, hence the episode title "Last of the Time Lords" and why he is to be an enemy.