Much of early television history is lost to us because it was aired live and therefore never recorded or recordings were not preserved. Doctor Who, which first aired in 1963, has this challenge as tapes were recorded over after production. About 100 of the 892 episodes are gone.
Occasionally, recordings surface. BBC News reports that two such episodes from 1965 have been found. They feature actor William Hartnell, who served as the first incarnation of the Doctor. The two episodes, titled "The Nightmare Begins" and "Devil's Planet," will air on Easter. They are part of the Daleks' Master Plan story arc, of which only half survives.
-via Gizmodo