He had previously worked as a script editor on The View from Daniel Pike as well as police series Barlow at Large and Z-Cars. His tenure on Doctor Who was one of the most troubled in the series' history. He was under orders from BBC management to reduce the levels of horror and violence that had become controversial under his predecessor, Philip Hinchcliffe, as well as having to cope with budget cuts, industrial action and a difficult relationship with Tom Baker in the lead role.
Despite the problems behind the scenes of the series at this time, Williams' era produced several popular additions to the Doctor Who legend, including the introduction of a robot dog as a companion, K9, the introduction of the Black and White Guardians in the Key to Time story arc and the introduction of the Doctor's Time Lady companion, Romana I.
Williams' tenure was also notable for the gradual introduction of more humour into the series, in particular the introduction of Douglas Adams as first a writer (The Pirate Planet) and then the script editor for the whole of season 17.
Due to a strike, Williams never completed the last story of season 17, Shada. Under the pseudonym "David Agnew", he co-wrote City of Death and The Invasion of Time and wrote the script and novelisation to The Nightmare Fair, which was intended to open season 23 before that season was substantially re-structured after Doctor Who went on hiatus. It was later adapted as an audio story by Big Finish Productions.
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