Nice thing! Hartnell to Troughton, Troughton to Pertwee, Pertwee to Baker (Tom), Baker to Davison, Davison to Baker (Colin), Baker to McCoy, McCoy to McGann, McGann to Hurt, Hurt to Eccleston, Eccleston to Tennant, Tennant to Smith, Smith to Capaldi! Simple, the thirteen incarnations of the Doctor.