Донна Ноубл
In "The Unicorn and the Wasp" (2008), Donna Noble compared Agatha Christie being surrounded by murders to meeting Charles Dickens at Christmas while he's surrounded by ghosts. The Doctor gave a "Well..." to a disbelieving Donna; Dickens was with his previous incarnation and Rose when the Gelth attempted to attack at Christmas, and the gaseous form of the Gelth could lead to their being classed "ghosts".