Conversation so far:
What work did Terry Nation do on Doctor Who?
Terry Nation made a significant contribution to the long-running BBC science-fiction series Doctor Who.
What contributions did Terry Nation make to Doctor Who?
Terry Nation made a significant contribution to Doctor Who, creating the villainous Daleks.
What was the name of the Doctor Who villains created by Terry Nation?
The Daleks are a fictional extraterrestrial race portrayed in the British science fiction television programme Doctor Who. The Daleks were conceived by science-fiction writer Terry Nation.
Did Terry Nation state how he came to create the characters of the Daleks?
Prior to his association with Hancock, Terry Nation had declined an offer from scriptwriter David Whitaker. Now unemployed, Nation accepted the offer, writing the Doctor Who serial, The Daleks.

Question: When was he hired to produce these characters for Doctor Who?
Self-contained rewrite: When was Terry Nation hired to produce the Dalek characters for Doctor Who?