The Doctor is a Time Lord: a 900 year old alien with 2 hearts, part of a gifted civilization who mastered time travel. The Doctor saves planets for a living—more of a hobby actually, and the Doctor's very, very good at it.
Rose
The End of the World
The Unquiet Dead
Aliens of London (1)
World War Three (2)
Dalek
The Long Game
Father's Day
The Empty Child (1)
The Doctor Dances (2)
Boom Town
Bad Wolf (1)
The Parting of the Ways (2)
Earth: Final Conflict
Life on Mars
Andromeda
Lockdown Zone: Level X
Infinity
Bring the Princess Home
Crusade
First Wave
Samurai Jack
Per Aspera
Don't Waste Your Time, Lovers
The Resilient Dr. Ling
Joseon Survival
Justice League
I Dream of Jeannie
Tale of the Nine Tailed 1938
神珑寄心
Journeyman
Far Out Space Nuts
Space Precinct