also retired the original howl-around title sequence used, with variations, from 1963 until 1973, introducing as its replacement the classic time tunnel special effects sequence which would run, until 1980, behind the opening and closing credits for every episode produced in seasons 11 to 17. When he was offered the chance to become producer on the series, Letts made it a condition that he be allowed to also continue to direct. The Head of Serials agreed to this, and Letts directed three Doctor Who serials during his time as producer: Terror of the Autons, Carnival of Monsters and Planet of the Spiders. Letts also directed most of the studio scenes for Inferno after Douglas Camfield was taken ill during the production. Letts's final work as a director on the series was when he returned in 1975 to direct The Android Invasion during the era of Philip Hinchcliffe as producer. Letts formed a particularly close partnership with two other contributors to the programme: Terrance Dicks, who was the script editor on the programme between 1968 and 1974; and playwright Robert Sloman, with whom Letts co-wrote four serials in the Pertwee era: The Dæmons (credited under the pen-name Guy Leopold); The Time Monster; The Green Death; and Planet of the Spiders, which was Pertwee's swansong. Letts later provided an official obituary for Sloman in December 2005, published in The Guardian. Letts was a Buddhist and also held liberal political views. According to Toby Hadoke, who contributed to his Guardian obituary, "Letts's liberal worldview led him to commission stories with contemporary resonance – eco-parables, critiques on colonialism and apartheid, even entry into the Common Market (the Galactic Federation in Doctor Who parlance) were all presented within a format of child-friendly derring-do." One of Letts' final tasks as producer was to cast Tom Baker as the Fourth Doctor. Baker was recommended to him by Bill Slater, an experienced former director who was then serving as the Head of Serials at the BBC. After one story with Baker, Robot, Letts left the position of producer in 1974, having been the longest serving producer on the programme until that time. In 1980, he returned to Doctor Who to be executive producer during John Nathan-Turner's first season as producer, between The Leisure Hive and Tom Baker's final story, Logopolis. Letts' return to the programme was because Nathan-Turner had not previously been either a director or producer, and