Instructions: Answer the question from the given passage. Your answer should be directly extracted from the passage, and it should be a single entity, name, or number, not a sentence.
Input: Passage: Since the 2005 revival, the Doctor generally travels with a primary female companion, who occupies a larger narrative role. Steven Moffat described the companion as the main character of the show, as the story begins anew with each companion and she undergoes more change than the Doctor. The primary companions of the Ninth and Tenth Doctors were Rose Tyler (Billie Piper), Martha Jones (Freema Agyeman), and Donna Noble (Catherine Tate) with Mickey Smith (Noel Clarke) and Jack Harkness (John Barrowman) recurring as secondary companion figures. The Eleventh Doctor became the first to travel with a married couple, Amy Pond (Karen Gillan) and Rory Williams (Arthur Darvill), whilst out-of-sync meetings with River Song (Alex Kingston) and Clara Oswald (Jenna Coleman) provided ongoing story arcs. The tenth series will introduce Pearl Mackie as Bill, the Doctor's newest traveling companion. Question: Since 2005, what is the gender of Doctor Who's primary traveling companion?
Output:
female