Lloyd became producer of Doctor Who in early 1966, midway through its third season, taking over after the brief, troubled tenure of John Wiles. His first credit as producer came on "The Celestial Toymaker".
Lloyd soon decided to shake up the TARDIS crew, feeling that the existing companions, space pilot Steven Taylor (Peter Purves) and schoolgirl Dodo Chaplet (Jackie Lane) were unsuitable as audience identification figures. He ordered them to be written out at the expiration of their contracts, which came at the end of Lloyd's third serial in charge ("The Savages") for Purves and mid-way through his fourth ("The War Machines") for Lane.
In their place, Lloyd cast Anneke Wills and Michael Craze as young adult contemporary Londoners Polly and Ben, designed to capture the mood of the Swinging Sixties and appeal more to contemporary audiences than their predecessors.
Lloyd was the first Doctor Who producer to oversee a regeneration, thus he can be credited for ensuring the show's longevity. While Lloyd's relationship with lead actor William Hartnell was nowhere near as acrimonious has his predecessor John Wiles' had been, Lloyd, like Wiles, was faced by the problem of Hartnell's declining health. Whereas Wiles had unsuccessfully tried to force Hartnell out against his wishes, Lloyd convinced Hartnell to step down from the show after "The Tenth Planet" and cast Patrick Troughton as his replacement.
Another decision made by Lloyd was to abolish the "pure historical" stories, with no science-fictional elements other than the TARDIS, which had been a staple of the show since its beginning. Troughton's second story, "The Highlanders" would be the final historical, as Lloyd moved the show towards focussing solely on "monster" stories, which he believed were more popular with the show's young target audience.
"The Highlanders" also saw the introduction of new companion Jamie McCrimmon, played by Frazer Hines. Originally written as a one-off guest character, Lloyd chose instead to add him to the TARDIS team as a full-time companion. He would go on to be the longest serving companion in the show's history by episode count, remaining all the way until the end of Troughton's tenure.
Lloyd then decided that Jamie made Ben surplus to requirements and instructed that he be writted out of the show a few stories later in "The Faceless Ones". Lloyd offered Anneke Wills the chance to stay on as Polly, but she opted to leave with Michael Craze. Deborah Watling was brought in as the new companion Victoria Waterfield in the following story "The Evil of the Daleks".
After nearly two years in charge, Lloyd moved on from Doctor Who in early 1968, handing over to his script editor Peter Bryant, who had already produced "The Tomb of the Cybermen" as a one-off before handing back to Lloyd, in order to demonstrate his suitability for the job. "The Enemy of the World" was the final story to credit Lloyd as producer.
