The Time Meddler is the ninth and final serial of the second season of the British science fiction television series Doctor Who. Written by Dennis Spooner and directed by Douglas Camfield, the serial was broadcast on BBC1 in four weekly parts from 3 to 24 July 1965. Set in Northumbria in 1066, before the Battle of Stamford Bridge, the serial features the time traveller the First Doctor (William Hartnell) and his companions Vicki (Maureen O'Brien) and Steven Taylor (Peter Purves) as they attempt to outwit the time traveller the Monk (Peter Butterworth), who is plotting to change the course of European history by wiping out King Harald Hardrada's Viking invasion fleet, leaving Harold Godwinson and the Saxon soldiers fresh to defeat William of Normandy and the Norman soldiers at the Battle of Hastings.

Spooner, who was leaving his role as story editor before this serial, was commissioned to write The Time Meddler by producer Verity Lambert. Spooner wanted the show to move away from full historical stories, instead hoping to blend them with futuristic serials. He studied the background of the Doctor in the writers' guide to create his antithesis, the Monk. The Time Meddler was the first serial under new story editor Donald Tosh, and the crew was joined during production by John Wiles, who was soon to replace Lambert as producer. The serial was produced at a low cost to offset the increased budget of the previous serial, The Chase; Camfield opted to forgo a traditional incidental score, instead using stock music and some percussive drumbeats played by Charles Botterill. The Time Meddler was the first serial to feature Purves in his main role as Steven, having been introduced in The Chase. Filming for the serial took place at Television Centre from June to July 1965.

The Time Meddler received a smaller audience than The Chase, with an average of 8.42 million viewers across the four episodes; the Appreciation Index also saw a drop. Contemporary and retrospective reviews were generally positive, with praise directed at performances of Hartnell and Butterworth, Spooner's script, and Camfield's direction, though the depiction of the villagers was criticised. The story was novelised and released on VHS, DVD, and as an audiobook. In 2020, it was voted the second-best First Doctor story by readers of Doctor Who Magazine.