William McIntyre

A man rode on the vehicle in the motorcade immediately behind John F. Kennedy's presidential limousine on 22 November 1963, the date of the President's assassination. Shortly before the assassination, the man was photographed with the occupants of the limousine in Dallas, Texas. He was stationed behind (TV: Rose) an agent of the Secret Service. (PROSE: Who Killed Kennedy) This photograph was retrieved from the Washington public archive in 2004 by Clive Finch, of interest to him because it featured the Ninth Doctor observing events. (TV: Rose)

Behind the scenes
The identity of the man, in the real world William "Tim" McIntyre, is not revealed in Rose.