Doctor Who bids farewell to its lead actors when the Doctor regenerates, but Patrick Troughton's regeneration scene as the Second Doctor wasn't clearly shown and instead left ambiguous. Doctor Who began airing on the BBC in 1963 and starred William Hartnell as the Doctor, a time-travelling alien who pilots a ship called the TARDIS.
In 1966, when Hartnell became too ill to continue, Patrick Troughton took over the role, with the recast being explained by a new plot device called regeneration, in
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