Background: Terence Joseph "Terry" Nation (8 August 1930 - 9 March 1997) was a Welsh television writer and novelist. Nation first made his name as a comedy writer before becoming a prolific writer for drama, working on many of the most popular British series of the 1960s and 1970s. He made a significant contribution to the long-running BBC science-fiction series Doctor Who from its outset, creating the villainous Daleks which established its early popularity and later devising the recurring character of Davros.
Context: Prior to this, Nation had declined an offer from scriptwriter David Whitaker to write for a new science-fiction programme that was entering production at the BBC; Whitaker had been impressed by a script that Nation had written for the ABC anthology series Out of this World. Now unemployed, and with a young family to support, Nation contacted Whitaker and accepted the offer, writing the second Doctor Who serial, The Daleks (also known as The Mutants and The Dead Planet). The serial introduced the eponymous extraterrestrial villains that would quickly become the series' most popular and enduring monsters, and resulted in a major merchandising success for the BBC.  Having risen in the public consciousness, Nation went on to contribute further scripts to Doctor Who. In 1965, Nation and Dennis Spooner co-wrote the 12-part serial The Daleks' Master Plan, after which Nation, who still held the copyright to the Daleks, attempted to launch a Dalek spin-off TV series in the United States. Various other Dalek tie-in material appeared, including comic strips in the children's weekly TV Century 21 and annuals; such material was frequently credited to Nation, even when written by others. Between 1966 and 1972, appearances by the Daleks in Doctor Who became less frequent and were written for the series by other authors.  In 1973, following an eight-year absence from scriptwriting for the series, Nation returned to writing for the Daleks on Doctor Who with the Third Doctor serial Planet of the Daleks. In 1998, readers of Doctor Who Magazine voted Nation's 1975 serial Genesis of the Daleks the greatest Doctor Who story of all time. In the story, Nation introduced the character of Davros, the creator of the Daleks, who went on to appear in further storylines.  Nation also wrote two non-Dalek scripts for Doctor Who, The Keys of Marinus in 1964, which introduced the Voord and The Android Invasion in 1975, which introduced the Kraal. During this time, Nation also worked in commercial TV, contributing scripts to series such as The Avengers, The Baron, The Champions, Department S, The Persuaders! and The Saint.  Nation's work on Doctor Who was the subject of the documentary Terror Nation, a special feature on the BBC DVD release of the serial Destiny of the Daleks.
Question: When did he start working on Doctor Who?

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