John Leeson signed on to voice a robot dog that was meant to last a single “Doctor Who” story, and ended up speaking for K9 for decades.
Leeson, the British actor whose voice made the robot dog K9 a fixture of the BBC science-fiction series “Doctor Who,” died on Sunday, Nov. 1, 2026. He was 83. His son, film editor Guy Ducker, 54, announced the death on Facebook.
“I regret to announce the death of my father, John Ducker, a.k.a. John Leeson, at 3.03pm today after a summer of illness. The end was peaceful,” Ducker wrote.
Russell T Davies, the former “Doctor Who” showrunner, led the tributes on Instagram, calling K9 “a posh dog, uppity, haughty, wry, but somehow innocent too, and so funny.”
David Tennant, who played the Doctor when K9 returned to the revived series in 2006, said Leeson gave the robot dog “something no special effect could supply, a personality that generations would love.”
From Hospital Porter to RADA
He was born John Francis Christopher Ducker in Leicester on March 16, 1943, the son of a clergyman. As a young man he joined the Leicester Drama Society.
Before he entered the Royal Academy of Dramatic Art in 1962, he worked as a hospital porter. He took Leeson as his professional surname and built his career in repertory theater.
The Dog Meant for One Story
K9 rolled into “Doctor Who” in the 1977 serial “The Invisible Enemy,” alongside Tom Baker’s Fourth Doctor. Writers Bob Baker and Dave Martin created the character for that story alone. Producer Graham Williams and script editor Robert Holmes saw the appeal, and Leeson’s performance helped turn a one-off prop into a recurring companion.
The machine came with a laser in its nose and the reply that generations of viewers can still recite: “Affirmative, Master.”
What kept it from being a novelty was the voice. Leeson’s clipped delivery leaned on comic timing rather than mechanical monotony, and the dry confidence played against Baker’s unpredictable Doctor. He once described K9’s personality as “pedantic arrogance and perky one-upmanship.” During rehearsals, Leeson sometimes moved around the studio on all fours so the other actors had something to play against.
The Voice That Kept Coming Back
Leeson voiced the character throughout Seasons 15 and 16, according to Big Finish Productions. He declined to return for Season 17, when David Brierley took the role, then came back for five serials in Season 18. K9’s regular appearances in the series ended in 1981.
That was not the end of it. Leeson returned for the 1981 spin-off pilot “K-9 and Company,” which starred Elisabeth Sladen as Sarah Jane Smith, and for the 1983 anniversary special “The Five Doctors.” He reunited with Sladen in the 2006 Tennant episode “School Reunion,” worked with her again on “The Sarah Jane Adventures,” and voiced K9 in “Journey’s End” in 2008. The audio dramas carried on, with Big Finish productions as recently as 2025.
Watson to Tom Baker’s Holmes
Leeson was also the original Bungle in the ITV children’s series “Rainbow” in 1972. His other television roles included “Dad’s Army,” “Blake’s 7,” “Crown Court,” “The Bill,” “Doctors,” “Sorry!” and “Longitude,” and he spent time as a Channel 4 continuity announcer.
Earlier in 2026, he and Tom Baker worked together again in a different pairing. Leeson played Dr. Watson opposite Baker’s Sherlock Holmes in the audio drama “Sir Sherlock.”
He is survived by his wife, Judy, and his son, Guy, who thanked the “Doctor Who” community for the support it had given his father’s work over the decades.
Ducker ended the announcement of his father’s death with a line from “Hamlet”: “Good night, sweet prince…”