All Creatures Great and Small was a BBC television series based upon the novels of James Herriot, which in turn were based on Herriot's life as a young veterinary surgeon working with Donald and Brian Sinclair (whose names were changed for the books to Siegfrried and Tristan Farnon) in and around Thirsk, Yorkshire just before and during the Second World War. It ran from 1978 to 1980. The leading role was taken by an unknown actor, Christopher Timothy, and Siegfried Farnon was played by Robert Hardy (most recently seen as Cornelius Fudge, Minister for Magic, in the Harry Potter movies). Tristan was played by Peter Davison, who became a household name as a result. Helen Herriot was played by Carol Drinkwater. Mary Hignett played the housekeeper Mrs Hall, and Margaretta Scott appeared as the recurring aristocratic dog-owner Mrs Pumphrey. Several actors recognizable from appearances on Doctor Who also guested on this series.
The series was John Nathan-Turner's first as full producer (his most recent previous credit had been as production unit manager on Doctor Who) and it also made a star of Peter Davison. JNT's experiences working with Davison led to his decision to offer him the role of the Doctor to succeed the departing Tom Baker. When an All Creatures special was produced some years later, the role of Helen was played by Lynda Bellingham, replacing Helen Drinkwater, who died from cancer. Bellingham later played the Inquisitor in the series of Doctor Who stories collectively known as "The Trial of a Time Lord."
Because of its many connections to the series, All Creatures has enjoyed a popularity with fans of Doctor Who. This is especially true of North American fans, as both series were widely syndicated together on PBS stations during the 1980s.