The Tenth Doctor travels alone during the time period 2008-2010.
 In the 2013 episode "The Time of the Doctor", the Eleventh Doctor clarifies that he is the product of the twelfth regeneration due to a previous incarnation that he chooses not to count and one other aborted regeneration
Since the 2005 revival, the Doctor generally travels with a primary female companion, who occupies a larger narrative role

