Agatha Christie

Agatha Christie was a famous human writer in the 20th century. The Doctor and Donna Noble meet her. (DW: The Unicorn and the Wasp)

In the episode Last of the Time Lords, The Doctor mentions that he would "love to meet Agatha Christie" just before Martha tells him she doesn't want to travel with him any more. She helps the Doctor and Donna solve the mystery in The Unicorn and the Wasp.