David Bradley, who played Argus Filch in the Harry Potter films, is to portray actor William Hartnell in the new, feature-length BBC Two drama about the start of Doctor Who, An Adventure in Space and Time.
Commenting on Bradley's performance as the first Doctor, An Adventure in Space and Time's writer and executive producer Mark Gatiss said: "David Bradley brings every ounce of his talent, humour and presence to the role of William Hartnell.
"It's a wonderfully touching and subtle performance and I'm immensely proud of both him and the film."
An Adventure in Space and Time is to celebrate the 50th anniversary of Doctor Who, which first aired on November 23 1963.
The cast of the drama also includes Call the Midwife star Jessica Raine as producer Verity Lambert; The Bourne Supremacy's Brian Cox as another BBC executive and Last Tango in Halifax's Sacha Dhawan as Waris Hussein, the director of the first Doctor Who episode.