Complex sentence: The Eleventh Doctor is an incarnation of the Doctor, the protagonist of the BBC television science fiction programme "Doctor Who", played by Matt Smith, in three series as well as seven specials, over an almost four-year period.
Split into simpler sentences: The Eleventh Doctor is an incarnation of the Doctor, the protagonist of the BBC television science fiction programme "Doctor Who". He is played by Matt Smith, in three series as well as seven specials, over an almost four-year period.