The news was shared on Facebook by his son, Guy Ducker, who wrote that his father's death came "after a summer of illness. The end was peaceful." In a separate post, Ducker thanked the Whovian community for the love shown to his father over the decades, saying it meant a great deal to both of them.

A role meant to last one episode

K9 was created by Bob Baker and Dave Martin and arrived in Doctor Who in 1977 in the Tom Baker story The Invisible Enemy. The robot dog was written for a single script only, but the production team believed the character would appeal to younger viewers and kept him in the Tardis team until 1981. For part of that run, David Brierly took over the voice.

Leeson later recalled being warned by BBC producers that nothing would follow the first episode, and joked in 2025 that playing the machine let him meet a tremendous number of knees. It was as K9 that he established the catchphrase "Affirmative, Master" when addressing the Doctor.

From Rada to the Tardis and beyond

Born John Ducker in 1943, he trained at Rada and went on to build a career on stage and screen. After leaving school he worked as a hospital porter before auditioning for drama school. He described his working life in interviews as two halves: mainly a stage actor, with the television work arising largely by accident.

His screen credits stretched widely:

• •Dad's Army, where he lamented the army haircut he was given, only for it to be hidden under a balaclava and tin hat anyway
• •the children's show Rainbow, where he played Bungle and said the hot studio work left him really ill inside the bear suit, poured out of the costume into a taxi every evening
• •Sorry!, Crown Court, Longitude, The Bill, Vanity Fair, Doctors and Blake's 7
• •a spell as a continuity announcer on Channel 4

Returns with Sarah Jane Smith

Leeson reprised K9 in Doctor Who's 20th anniversary special and in the spin-off K-9 and Company, which featured Elisabeth Sladen as Sarah Jane Smith. He and Sladen were reunited in the 2006 David Tennant episode School Reunion, and the pair later featured in the CBBC spin-off The Sarah Jane Adventures, which ran from 2007 until Sladen's death in 2011.

Tributes from the Doctor Who family

Former showrunner Russell T Davies said on Instagram that asking John to provide the voice for the returning robot was never in doubt, and praised it as pitched perfectly so that children could impersonate the character. "A true gent, and a great loss," Davies wrote.

Keith Barnfather, a producer of Doctor Who behind-the-scenes documentaries who first worked with Leeson in the 1980s, remembered him as "kind, considerate, professional, charming, talented, unassuming". Lisa Bowerman, whose credits span the Doctor Who universe, called him an utterly lovely man and a truly iconic voice.

Leeson's connection to the role ran to the end of his life: he was still voicing K9 for Big Finish audio dramas last year, at the age of 82.