Nickname of Dr. Remy Hadley (Olivia Wilde). Derived from the fact that it was her number when House labeled tagged the fellowship applicants for his team in Season 4, starting with "The Right Stuff." House never seems to have bothered learning her name, or at least fakes it well: he acts puzzled when Foreman mentions it in "Big Baby," a year later. When referring to her indirectly, the other team members call her Thirteen as well. Usually they don't use her real name or Thirteen when talking to her directly.