Donna Noble . Portrayed by British actress and comedian Catherine Tate , she is a companion of the Tenth Doctor ( David Tennant ) . Originally appearing in the closing scene of the show 's 2006 series and as a special guest star in its following Christmas special , `` The Runaway Bride '' , Tate was not expected to reprise her role as Donna ; for series 3 ( 2007 ) , the Doctor travelled alongside medical student Martha Jones ( Freema Agyeman ) . Although she at first finds alien time traveller the Doctor terrifying , their initial encounter leaves her unsatisfied with her normal life and she decides to travel alongside him when the next opportunity arises . Donna becomes an asset to the Doctor on his adventures and it is she who ultimately saves the universe in the series 4 finale , although tragically at the cost of the memories of her travels with the Doctor . In a contrast to the Tenth Doctor 's prior companions , who both harboured romantic feelings for him , Donna and the Doctor shared a strictly friendly relationship ; and she did not feel the need to prove herself to be allowed to travel with the Doctor , who refers to her as his `` best mate '' .
Donna Noble travels with the Doctor.