Ronald Reagan

 was a President of the United States. According to the Eighth Doctor, he was the direct successor to Jimmy Carter. (EDA: Interference - Book One) His indirect successor from the 1990s, Tom Dering, once speculated that either Carter or he must have secretly constructed Station Nine. (EDA: Option Lock).
 * Reagan's first name wasn't used in either Option Lock or Interference, but the common-sense interpretation of the two passages is that the authors were describing the real-life President Ronald Reagan.