After a half-century of travelling through time and space, the British Broadcasting Corporation (BBC)’s crowning gem “Doctor Who,” celebrates its 50th anniversary with a special-length episode to be aired Saturday. What began as a family-oriented program in the early sixties has since become an international cult sensation and the longest-running sci-fi show in television history.

11 distinct actors have played the part of the alien Time Lord on TV, with a twelfth appearing on Saturday, and the thirteenth to make his debut on Christmas. The titular character’s ability to regenerate upon death has allowed producers to cultivate an entire cast of actors for the single role. This plot device, which came about after the original Doctor fell ill, is responsible in part for the show’s longevity.
After the series went on hiatus in 1989, it was revived in 2005 with fresh faced actors and (debatably) better special effects to appeal to a new generation of avid viewers. This Saturday’s hour-and-fifteen-minute episode is confirmed to star the show’s current lead, Matt Smith, and former Doctor David Tennant with the possibility of more surprise appearances.