John Leeson, who has died aged 83, was a genial character actor who provided the voice of the much-loved robotic sidekick K9 in the popular BBC TV series Doctor Who. Originally conceived to appear in just one story, The Invisible Enemy, in 1977, K9 was a mobile, dog-shaped computer who produced ticker-tape information from his mouth and had a laser gun in his nose. With a pinched voice, clipped delivery and a tendency towards pedantry, he served as both encyclopedia and guard dog, and was deemed successful enough a creation to retain as a regular character.

K9 was the perfect foil for Tom Baker’s spiky, obtuse Time Lord: Leeson likened the character to King Lear’s fool – a wise and funny factotum licensed to call out his master’s faults and prick his pomposity. Off-screen Baker thought highly of Leeson, and felt that the intelligent, unassuming and witty actor was more interesting that the oft-malfunctioning K9 prop, which caused many delays on the studio floor. Leeson also won the appreciation of his colleagues by attending rehearsals and gamely performing on all fours.

During his K9 stint he also appeared in the flesh in Doctor Who as an undercover environmentalist in The Power of Kroll (1978). He left the show briefly but returned for a final season in 1980 and continued voicing the “tin dog” for the next 45 years, taking in K9 and Company (a broadcast pilot for his own series, 1981), audio adventures for Big Finish Productions (2003-2026), the successful Doctor Who revival opposite David Tennant (2006, 2008), the popular spin-off The Sarah Jane Adventures (2007-2010), and an Australian children’s series, K9 (2009-10).

He also made in-character contributions, improvising his lines, to episodes of Blue Peter (1977, 2006), The Weakest Link (2007) and Pointless Celebrities (2013) among many other related engagements. Leeson’s own warm, gentle, silvery tones were also put to great effect as a reader of Doctor Who audiobooks.

He was born John Ducker in Leicester, the second of three children of Eric Ducker, the vicar at St Margaret’s church (and later canon of Leicester Cathedral), and his wife, Barbara (nee Payne), a keen amateur actor. John showed an aptitude for performance from an early age, and won a choral scholarship to the Pilgrims’ school at Winchester Cathedral.

He struggled there and at another preparatory school, where he was bullied, before finding solace in drama – discovering welcome refuge when immersing himself in other characters – as a pupil at Bryanston school in Dorset. Playing Feste in a school production and visiting Stratford-Upon-Avon to watch Twelfth Night confirmed his desire to become an actor.

After a brief spell as a hospital porter he was accepted by Rada in London, where he adopted his stage name in acknowledgement of a kindly godmother. He graduated in 1964 and immediately went into repertory theatre at Frinton-on-Sea. His myriad subsequent theatre engagements included the first West End production of Plaza Suite (Lyric theatre, 1969) and taking over from Brian Cox in Don’t Start Without Me (Garrick theatre, 1971).

His television debut – as a French hippy in the soap opera Crossroads – came in 1967, and in 1972 he was the original Bungle the Bear in the first 50 episodes of the fondly remembered children’s programme Rainbow. An adept light comedian, he appeared in Dad’s Army (1969), Sorry! (1981) and ‘Allo ‘Allo (1989), and his drama credits included Blake’s 7 (in two different roles, 1978 and 1979), Bugs (1995) and Longitude (2000).

His improvisational skills were watched by millions when he was one of the regular coterie of actors who helped the prankster Jeremy Beadle spring elaborate hoaxes on unsuspecting members of the public in Beadle’s About (1986-92) and he also appeared in the films Tarka the Otter (1979) and Whoops Apocalypse (1987).

Possessed of genuine curiosity and an eclectic array of knowledge, he was a man of many interests and talents – from being a continuity announcer on the BBC and Channel 4 to serving as a justice of the peace at Ealing magistrates’ court for 25 years. He was an accredited wine educator; a respected member of the Circle of Wine Writers who lectured on cruises and advised at tastings.

He was a skilled cook whose prize for winning a Radio Times and BBC recipe competition was a trip to the Cipriani hotel in Venice in the company of one of its judges, Antonio Carluccio. He used his advanced culinary skills and knowledge of period gastronomy to assist his wife, Judy – a production buyer for major film and television productions – by providing accurately rendered food spreads for shows such as Poirot (1993) and Foyle’s War (2002).

He also wrote an autobiography, Tweaking the Tale (2013) and a cookbook, Dog’s Dinners (2014).

He is survived by Judy (nee Griffiths), whom he married in 1969, and their son, Guy.

• John Leeson (John Francis Christopher Ducker), actor, born 16 March 1943; died 1 November 2026