The actor John Leeson, the voice of K-9, has died at the age of 83.

John Leeson played the voice of the Doctor's robot dog in 54 episodes of Doctor Who.  His characterisation of the little robot dog was so skilled and so full of fun that he helped make what was due to be a temporary character into a fully fledged member of the TARDIS crew, much loved and remembered by fans. It is a tribute to the actor that his cry of Affirmative is as much associated with Doctor Who as the Daleks' cry of Exterminate. He endowed the character with a life force that saw K-9 return to the series and its spinoffs many times over the years. 

John Leeson was born John Ducker in 1943. In the 1950s, he joined the Leicester Dramatic Society before winning a place at the Royal Academy of Dramatic Art in London. At RADA, he adopted the stage name John Leeson, derived from the surname of a wealthy godmother whom he believed was funding his tuition.

After graduating, he worked in repertory and pantomimes, including a production of Toad of Toad Hall, in which he met his future wife.

His first work in television was as a walk-on in a BBC play The Wedding Feast in 1965, followed by The Spanish Farm and Dad's Army in 1968. He played the original Bungle the Bear in the children's series Rainbow. 

In 1977, he was asked to play two voices in the fourth Doctor story, The Invisible Enemy. One was the voice of the Nucleus, the other a fun character, Professor Marius's robot dog K-9. Because the electronic prop was unavailable for the rehearsal period, Leeson got down on his hands and knees and physically ran around the rehearsal room acting as K9.

His voice for the character was so successful that the producer Graham Williams decided to make the character a regular and put Leeson on contract to provide the voice.  

Leeson would stay with the series for the next two years, appearing on screen as the character Dugeen in the story The Power of Kroll, a story where K-9 does not appear. He left at the end of The Armageddon Factor, fearing that he would lose work if he remained firmly off-screen. 

The character of K-9 remained in the series, voiced by David Brierley for season 17, but for season 18, Leeson was back behind the microphone, guiding the character until it was written out at the end of the 1981 story Warriors' Gate. 

K-9 and Leeson would be back at the end of the year in the spin-off starring Elisabeth Sladen, K-9 and Company and in the 20th Anniversary special The Five Doctors. in 2006, when Russell T. Davies was writing an episode, School Reunion, dealing with the return of Sarah Jane Smith, he also brought back John Leeson as K-9.  Over the next 15 years, Leeson would reprise his portrayal of K-9 on many occasions, including in The Sarah Jane Adventures, the K-9 series and many Big Finish audio adventures. 

Away from Doctor Who, John Leeson made many memorable appearances on British television, including roles in Blake's 7, Jigsaw, Crown Court,  The Barretts of Wimpole Street,  Minder, Vanity Fair and Doctors. 

John Leeson died peacefully earlier today after a short illness. He is survived by his wife Judy Griffiths and their son, filmaker Guy Ducker