Derek Acorah

In 2007, after "ghosts" started appearing across Earth, Derek Acorah proclaimed on television, "Well, no-one needs me any more." (TV: Army of Ghosts)

Behind the scenes
Though not directly mentioned in the episode, in the real world, Acorah worked as a medium on shows such as at the time Army of Ghosts aired. The gag here was that as "ghosts" started appearing, this would have meant his job was now obsolete.