David Tennant's incarnation of The Doctor is particularly light-hearted... at least on the surface. The Tenth Doctor's persona seems to have a tendency to babble, mixing apparent nonsense with nuggets of vital information. He develops closer ties than ever with his companions, their friends and family than he ever did in any of his previous versions.
However, beneath the surface this version of the Time Lord reveals intense emotions in play. One of this Doctor's recurring lines is the fact that he is "so sorry" for what has occurred - or what is going to occur. The shows begins to explore the loneliness of the character, with Time Lord longevity described as a curse - while his human companions all someday leave him and eventually die, he continues on.
The Tenth Doctor wears a four-buttoned suit, a shirt and a tie, a light brown overcoat (reportedly given to him by Janis Joplin) and trainers. He also dons a pair of glasses from time to time - and even a pair of red-blue 3D glasses! The character speaks with an Estuary English accent - unlike Tennant whose natural accent is Scottish English...
Taking over from Ecclestone in 2005, Tennant would appear in 36 stories (47 episodes) until handing over to Matt Smith in early 2010.