Its British serial from 1963.year but since 2005.they made modern version
. Its about alien,but he looks more like human,he has 2 hearts and he is traveling throught time and space in blue police box called TARDIS(Time and relative dimension in space). Doctor usually travels with some companion,most of them leave him because of some reasons example some of them get married or some of them even died when they traveled and had fight. there were 11. Doctors. Doctor can regenarate when he is about to die,but he dont die he regenarate and change his face. 10th Doctor was David Tennant
and 11th Doctor is Matt Smith ♥ ♥...but soon he is leaving and 12th Doctor will be Peter Capaldi.
Here on wikipedia you can read more about Doctor Who